3.3.7 Optical isomerism

Define optical isomerism and explain how it occurs from chirality

Describe how asymmetric carbon atoms are chiral and how this can give rise to optical isomers

Draw the structural and displayed formulas of enantiomers

Understand how racemic mixtures (racemates) are formed and why they are optical isomers

1. (a) Consider the following pair of isomers.

(i) Name compound C.

...........................................................................................................................

(ii) Identify a reagent which could be used in a test-tube reaction to distinguish between C and D. In each case, state what you would observe.

Reagent ............................................................................................................

Observation with C ..........................................................................................

Observation with D........................................................................................... (4)

(b) Consider the following pair of isomers.

(i) Name compound E.

...........................................................................................................................

(ii) Identify a reagent which could be used in a test-tube reaction to distinguish between E and F. In each case, state what you would observe.

Reagent ............................................................................................................

H C HO COCH CH

O O

CH CH CH CH2 22 23 3

C D

H C C H CCH CH

O O

CH CH CH CH CH2 22 2 23

3

3

E F

Observation with E ..........................................................................................

Observation with F........................................................................................... (4)

(c) Draw the structure of the chain isomer of F which shows optical isomerism.

(1)

2. (a) Addition reactions to both alkenes and carbonyl compounds can result in the formation of isomeric compounds.

(i) Choose an alkene with molecular formula C4H8 which reacts with HBr to form two structural isomers. Give the structures of these two isomers and name the type of structural isomerism shown.

Outline a mechanism for the formation of the major product.

(ii) Using HCN and a suitable carbonyl compound with molecular formula C3H 6O, outline a mechanism for an addition reaction in which two isomers are produced. Give the structures of the two isomers formed and state the type of isomerism shown.

(14)

Q3. Which one of the following reaction mixtures would give a product capable of exhibiting optical isomerism?

A CH3CH=CH2 + HBr

B CH3CH2CH2Br + NaOH

C CH3CH2CH2OH + H2SO4

D CH3CH2 CHO + HCN (Total 1 mark)

Q4.On reduction, a racemate can be formed by

A CH3CH2CH2CH2CHO

B CH3CH2CH2COCH3

C CH3CH2COCH2CH3

D CH3CH=CHCH2CHO (Total 1 mark)

Q5. (a) P, Q and R have the molecular formula C6H12

All three are branched-chain molecules and none is cyclic. P can represent a pair of optical isomers. Q can represent a pair of geometrical isomers. R can represent another pair of geometrical isomers different from Q.

Draw one possible structure for one of the isomers of each of P, Q and R.

Structure of P

Structure of Q

Structure of R (3)

(b) Butanone reacts with reagent S to form compound T which exists as a racemic mixture. Dehydration of T forms U, C5H7N, which can represent a pair of geometrical isomers.

(i) State the meaning of the term racemic mixture and suggest why such a mixture is formed in this reaction.

Racemic mixture ________________________________________________

_______________________________________________________

Explanation ____________________________________________________

_______________________________________________________

(ii) Identify reagent S, and draw a structural formula for each of T and U.

Reagent S _____________________________________________________

Compound T

Compound U

(6)

Q6. Which one of the following reactions will produce an organic compound that has optical isomers?

A dehydration of butan-2-ol by heating with concentrated sulphuric acid

B reduction of pentan-3-one by warming with NaBH4

C addition of Br2 to 3-bromopropene

D reduction of 2,3-dimethylpent-2-ene with H2 in the presence of a nickel catalyst

(Total 1 mark)

Q7. Which one of the following can exhibit both geometrical and optical isomerism?

A (CH3)2C=CHCH(CH3)CH2CH3

B CH3CH2CH=CHCH(CH3)CH2CH3

C (CH3)2C=C(CH2CH3)2

D CH3CH2CH(CH3)CH(CH3)C=CH2

(Total 1 mark)

Q8. Which compound forms optically active compounds on reduction?

A CH3CH2C(CH3)=CHCH3

B CH3CH2C(CH3)=CH2

C CH3COCH3

D CH3CH2COCH3 (Total 1 mark)

3.3.8 Aldehydes and ketones

Recall aldehydes are readily oxidised to carboxylic acids

Recall Fehling's solution and Tollens' reagent can be used to distinguish between aldehydes and ketones

Write overall equations for reduction reactions using [H] as the reductant

Outline the nucleophilic addition mechanism for reduction reactions (aldehydes to primary alcohols; ketones to secondary) with NaBH4 (nucleophile shown as H-)

Write overall equations for the formation of hydroxynitriles using HCN

Outline the nucleophilic assition mechanism for the reaction with KCN followed by dilute acid

Explain why nucleophilic addition reactions of KCN, followed by dilute acid, can produce a mixture of enantiomers

Outline the hazards of using KCN

3.3.9 Carboxylic acids and derivatives

Outline the structures of carboxylic acids and esters

State carboxylic acids are weak acids, but will liberate CO2 from carbonates

State the reaction between carboxylic acids and alcohols to produce etsers

Outline the common uses of esters

State vegetable oils and animal fats are esters of propane-1,2,3-triol and can be hydrolysed in alkaline conditions to give soap and glycerol Esters can be hydrolised in acid or alkaline conditions to form alcohols and carboxylic acids or salts of carboxylic acids Understand biodiesel is a mixture of methyl esters of long-chain carboxylic acids and is produced by reacting vegetable oils with methanol in the presence of a catalyst

Outline the strudtures of acid anhydrides, acyl chlorides and amides

Outline the mechanism of nucleophilic addition-elimination reactions of acyl chlorides with water, alcohols, ammonia and primary amines

Q1. Butenedioic acid, HOOCCH=CHCOOH, occurs as two stereoisomers. One of the isomers readily forms the acid anhydride C4H2O3 when warmed.

(a) Draw the structures of the two isomers of butenedioic acid and name the type of isomerism shown. Use the structures of the two isomeric acids to suggest why only one of them readily forms an acid anhydride when warmed. Draw the structure of the acid anhydride formed.

(6)

(b) Identify one electrophile which will react with butenedioic acid and outline a mechanism for this reaction.

(4)

(c) Write an equation for a reaction which occurs when butenedioic acid is treated with an excess of aqueous sodium hydroxide.

(2)

(d) Describe and explain the appearance of the proton n.m.r. spectrum of butenedioic acid.

(3) (Total 15 marks)

Q2.Which one of the following is not a correct general formula for the non-cyclic compounds listed?

A alcohols CnH2n+2O

B aldehydes CnH2n+1O

C esters CnH2nO2

C primary amines CnH2n+3N (Total 1 mark)

Outline the industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of the drug aspirin REQUIRED PRACTICAL 10: Preparation of a pure organic solid and test of its purity; a pure organic liquid

Q3. (a) Ester X, CH3CH2COOCH3, can be produced by the reaction between propanoyl chloride and methanol. Name X and outline a mechanism for this reaction. Name the mechanism involved (6)

(b) The proton n.m.r. spectrum of X is shown below together with that of an isomeric ester, Y. Deduce which of Spectrum 1 and Spectrum 2 is that obtained from X. Use Table 1 on the Data Sheet and the integration data on the spectra to help you to explain your deduction. Suggest a structure for Y.

(4)

(Total 10 marks)

Q4.Propanone can be reduced to form an alcohol. A functional group isomer of the alcohol formed is

A CH3CH2CH2OH

B CH3CH2CHO

C CH3OCH2CH3

D CH3COCH3

(Total 1 mark)

Q5. Compounds C and D, shown below, are isomers of C5H10O

C D

(a) Name compound C.

......................................................................................................................

(1)

(b) Use Table 2 on the Data Sheet to help you to answer this question.

(i) Suggest the wavenumber of an absorption which is present in the infra-red spectrum of C but not in that of D.

.............................................................................................................

(ii) Suggest the wavenumber of an absorption which is present in the infra-red spectrum of D but not in that of C.

............................................................................................................. (2)

(c) Deduce the number of peaks in the proton n.m.r. spectrum of C.

...................................................................................................................... (1)

(d) Identify a reagent that you could use to distinguish between C and D. For each of C and D, state what you would observe when the compound is treated with this reagent.

Reagent .......................................................................................................

Observation with C .......................................................................................

Observation with D ....................................................................................... (3)

(e) Compound E, CH3CH2CH2CH2CHO, is also an isomer of C5H10O

Identify a reagent which will react with E but not with C or D. State what you would observe when E is treated with this reagent.

Reagent .......................................................................................................

Observation with E ....................................................................................... (2)

(Total 9 marks

Q6.Propanoic acid reacts with methanol in the presence of a small amount of concentrated sulphuric acid. The empirical formula of the ester formed is

A CH2O

B C2H6O2

C C2H4O2

D C2H4O (Total 1 mark)

7 (a) (i) Name alcohol X.

...........................................................................................................................

(ii) Name and outline the mechanism for the reaction occurring when alcohol X is converted into 2,3-dimethylbut-2-ene in the presence of a strong acid.

Name of mechanism.............................................................................................

Mechanism

(iii) Give the structure of, and name an isomer of 2,3-dimethylbut-2-ene which is also formed in the reaction. Explain why two products are obtained.

Structure

Name of isomer.................................................................................................

Explanation ......................................................................................................

...........................................................................................................................

...........................................................................................................................

(10)

(b) (i) Write an equation for the reaction between alcohol X and ethanoyl chloride. Name and outline a mechanism for this reaction, using ROH to represent the alcohol in the mechanism.

Equation

Name of mechanism............................................................................................

Mechanism

(ii) Give an alternative method for obtaining the organic reaction product in part (b) (i), starting from alcohol X, other than using ethanoic anhydride.

State the type of reaction, the reagent(s) used and the reaction conditions.

Type of reaction. ...............................................................................................

Reagent(s)..........................................................................................................

Conditions......................................................................................................... (9)

3.3.10 Aromatic chemistry

State the nature of the bonding in a benzene ring

Delocalisation of p-electrons and the link to stability

Use thermochemical evidence from enthalpies of hydrogenation to account for this stability

Explain why substitution reactions occur in preference to addition reactions

Outline the electrophilic substitution mechanisms of: nitration, including the generation of the nitronium ion

Outline the electrophilic substitution mechanisms of: acylation using AlCl3 as a catalyst

3.3.11 Amines Preparation of primary aliphatic amines by the reaction of ammonia with halogenoalkanes and reduction of nitriles

Preparation of aromatic amines by the reduction of nitro compounds, used in the preparation of dyes

State amines are weak bases and nucleophiles

Explain the difference between base strength in terms of the availability of the lone pair of electrons in the N atom

Outline the mechanisms of nucleophilic substitution of ammonia and amines with halogenoalkanes

The use of quaternary ammonium salts as cationic surfactants

Outline the mechanisms of the nucleophilic addition-elimination reactions of ammonia and primary amines with acyl chlorides

1. 5-Amino-2-methylbenzenesulphonic acid can be obtained from methylbenzene in a three-step synthesis:

(a) For each step below, name the type of reaction taking place and suggest a suitable reagent or combination of reagents.

Step 1

Type of reaction .........................................................................................................

Reagent(s) ..................................................................................................................

Step 3

Type of reaction .........................................................................................................

Reagent(s) ...................................................................................................................

(4)

(b) Write an equation for the formation of the reactive inorganic species involved in the mechanism in Step 1.

.................................................................................................................................... (2)

(Total 6 marks)

2. Consider the following reaction sequence:

(a) Give the reagents required to carry out Step 1 and write an equation for the formation of the reactive intermediate involved. Name and outline the mechanism for the reaction between this intermediate and benzene.

Reagents ....................................................................................................................

.......................................................…….......................................................................

Equation for formation of reactive intermediate ...............................................…....

.......................................................……......................................................................

CH 3 CH 3 CH 3 CH 3

3 3Step 1 Step 2 Step 3

NO NO NH2 2 2

SO H SO H

COCH C H2 26 6 65 5 5CH(OH)CH C H CH=CHC H

Step 1 Step 2 Step 3

.

Name of mechanism ...............................................................................................…..

Mechanism

(8)

(b) Name the type of reaction taking place in Step 2 and suggest a suitable reagent or combination of reagents.

Type of reaction .........................................................................................................

Reagent(s) ................................................................................................................. (2)

(c) Suggest a suitable reagent for Step 3 and name the mechanism for this reaction.

Reagents ....................................................................................................................

Name of mechanism ...............................................................................................…..

(2)

(d) What type of stereoisomerism is shown by the product of Step 2?

.......................................................…….......................................................................

(1)

(e) Name the type of isomerism shown by the final product, 1,2-diphenylethene, and explain why this compound can exist in two stereoisomeric forms.

Type of isomerism .......................................................................................................

Explanation ...............................................................................................................

.......................................................…….......................................................................

(2) (Total 15 marks)

3. (1-Methylpropyl)benzene, C6H5CH(CH3)CH2CH3, is the major organic product obtained when benzene and but-l-ene react together in the presence of aluminium chloride and hydrogen chloride.

(a) Write an equation showing the formation of the major carbonium ion obtained from but-l-ene, aluminium chloride and hydrogen chloride.

...................................................................................................................................

................................................................................................................................... (2)

(b) Name the mechanism involved in the reaction between benzene and the carbonium ion formed in part (a) above.

................................................................................................................................... (1)

(c) Explain why butylbenzene, C6H5CH2CH2CH2CH3, is obtained only as a minor by-product in the above reaction between benzene and but-l-ene.

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

................................................................................................................................... (3)

(d) Explain why only one organic product is obtained when but-2-ene is used instead of but-l-ene in the reaction with benzene.

...................................................................................................................................

................................................................................................................................... (1)

(e) Give the structure of a compound, other than an alkene, which could be used to make (1-methylpropyl)benzene from benzene in the presence of aluminium chloride.

(1)

(Total 8 marks)

4. (a) In the laboratory, phenylethene can be obtained from benzene in a three-step synthesis:

(i) Give the organic reagent and the inorganic catalyst used in Step 1.

Step 1 Step 2 Step 3

COCH CH(OH)CH CH CH 23

Reagent .............................................................................................................

Catalyst ............................................................................................................

(ii) Name the type of reaction taking place in Step 2.

..........................................................................................................................

(iii) Suggest either a reagent or a combination of reagent and catalyst suitable for the conversion in Step 2.

..........................................................................................................................

(iv) For Step 3, name the type of reaction and suggest a suitable reagent for the reaction.

Type of reaction ...............................................................................................

Reagent .............................................................................................................

(6)

(b) In industry, phenylethene is made from benzene and ethene in a two-step process:

(i) Give one major use of phenylethene.

.........................................................................................................................

(ii) Identify the reactive species which attacks benzene in Step 1 and write an equation to show how this species is generated.

Reactive species ...............................................................................................

Equation ...........................................................................................................

(iii) Name the type of reaction which occurs in Step 2.

.......................................................................................................................... (4)

(Total 10 marks)

5. (a) Outline a mechanism for the reaction of CH3CH2CH2CHO with HCN and name the product.

Mechanism

Step 1 Step 2

CH CH CH CH22 3

Name of product ......................................................................................................... (5)

(b) Outline a mechanism for the reaction of CH3OH with CH3CH2COCl and name the organic product.

Mechanism

Name of organic product ............................................................................................

(5)

(c) An equation for the formation of phenylethanone is shown below. In this reaction a reactive intermediate is formed from ethanoyl chloride. This intermediate then reacts with benzene.

(i) Give the formula of the reactive intermediate.

...........................................................................................................................

(ii) Outline a mechanism for the reaction of this intermediate with benzene to form phenylethanone.

(4)

(Total 14 marks)

33

3+ CH COCl COCH + HClAlCl

6. Consider the following reaction sequence:

(a) For each step, name the type of reaction taking place and suggest a suitable reagent or combination of reagents.

Step 1

Type of reaction..........................................................................................................

Reagent(s)...................................................................................................................

Step 2

Type of reaction..........................................................................................................

Reagent(s)...................................................................................................................

Step 3

Type of reaction..........................................................................................................

Reagent(s)................................................................................................................... (7)

(b) What type of stereoisomerism is shown by the product of Step 2?

.................................................................................................................................... (1)

(c) Explain why the final product, 1-phenylpropene, is formed as a mixture of two isomers.

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (2)

7 . When 1-phenylpropene is treated with hydrogen bromide, two compounds are formed which are structural isomers.

(i) Give the structures of the two isomers.

Isomer 1 Isomer 2

Step 1 Step 2 Step 32 3COCH CH 2 3CH(OH)CH CH 3CH=CHCH

(ii) Name the type of mechanism involved.

........................................................................................................................

(iii) By reference to the structures of the two carbonium ion intermediates formed, suggest why the two isomers are obtained in unequal amounts.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................ (6)

(Total 16 marks)

8. (a) Name the compound (CH3)2NH

..................................................................................................................................... (1)

(b) (CH3)2NH can be formed by the reaction of an excess of CH3NH2 with CH3Br. Name and outline a mechanism for this reaction.

Name of mechanism .....................................................................................................

Mechanism

(5)

(c) Name the type of compound produced when a large excess of CH3Br reacts with CH3NH2 Give a use for this type of compound.

Type of compound .......................................................................................................

Use ..............................................................................................................................

(2)

(d) Draw the structures of the two compounds formed in the reaction of CH3NH2 with ethanoic anhydride.

(2)

(Total 10 marks)

9. (a) Name and outline a mechanism for the formation of butylamine, CH3CH2CH2CH2NH2, by the reaction of ammonia with 1-bromobutane, CH3CH2CH2CH2Br.

Name of mechanism .....................................................................................................

Mechanism

(5)

(b) Butylamine can also be prepared in a two-step synthesis starting from 1-bromopropane, CH3CH2CH2Br. Write an equation for each of the two steps in this synthesis.

Step 1

.....................………………………………………………………………………….

Step 2

.....................………………………………………………………………(3)

(c) (i) Explain why butylamine is a stronger base than ammonia.

...........………………………………………………………………….

...........…………………………………………………………………….

...........………………………………………………………………………

(ii) Identify a substance that could be added to aqueous butylamine to produce a basic buffer solution.

...........……………………………………………………………………… (3)

(d) Draw the structure of a tertiary amine which is an isomer of butylamine.

10. The figure shows a reaction scheme for some aromatic compounds.

(a) (i) Give the reagents and conditions for the conversion of benzene into compound P.

...........................................................................................................................

...........................................................................................................................

(3)

(ii) Give the name of the mechanism of this reaction.

...........................................................................................................................

(2)

(b) Draw the graphical formulae of the possible organic products when excess chlorine is passed through boiling compound P in strong sunlight.

(3)

(c) (i) Classify the type of reaction occurring when nitrobenzene is converted into compound Q.

...........................................................................................................................

(1)

(ii) Draw the graphical formula of compound Q.

CH 3

benzene compound P

NO2

concentrated H SO /concentrated HNO at 55 ºC

42

3

Sn/HCl(aq)compound Q

nitrobenzene

(2)

(d) Classify the types of reaction and draw the graphical formulae of the organic products of the reaction of propanal with:

(i) sodium tetrahydridoborate(III), NaBH4;

Type of reaction ............................................................................................... (2)

(ii) Fehling’s solution;

Type of reaction ............................................................................................... (2)

(iii) hydrogen cyanide.

Type of reaction ............................................................................................... (2)

(Total 17 marks)

11. (a) Explain how methylamine can act as a Brønsted-Lowry base.

....................................................................................................................................

....................................................................................................................................

(2)

(b) Explain why phenylamine is a weaker base than ammonia.

....................................................................................................................................

....................................................................................................................................

(2)

(c) (i) Name the type of mechanism involved when methylamine is formed from bromomethane and ammonia.

...........................................................................................................................

(ii) Give the structures of three organic compounds other than methylamine which can be obtained from the reaction between an excess of bromomethane and ammonia.

Compound 1 Compound 2 Compound 3

(iii) Name the type of compound formed in part (c)(ii) which can be used as a cationic surfactant.

...........................................................................................................................

(5) (Total 9 marks)

12. (a) (i) Write an equation for the formation of ethylamine from ethanenitrile.

.......................................................................................................................... (ii) Suggest a suitable reagent or a combination of reagent and catalyst for

this reaction.

.......................................................................................................................... (2)

(b) State the type of reaction taking place between ethylamine and an excess of bromoethane. Give the structures of the three organic products obtained from this reaction.

Type of reaction...........................................................................................................

Product 1 Product 2 Product 3

(4)

(c) Suggest a mechanism to show how molecules of ethylamine and hydrogen bromide react together.

(3)

(d) Explain why phenylamine is a weaker base than ethylamine.

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (2)

(e) Suggest why ethanamide, CH3CONH2, is a weaker base than ethylamine.

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (2)

13. Write an equation for the formation of the compound CH3CONHCH2CH3 from ethylamine and a suitable reagent. Name and outline the mechanism for this reaction.

Equation .....................................................................................................................

Name of mechanism ...................................................................................................

Mechanism

(7)

(Total 20 marks)

14. (Phenylmethyl)amine, C6H5CH2NH2, can be prepared from (bromomethyl)benzene, C6H5CH2Br, and also from benzenecarbonitrile, C6H5CN.

(a) (i) Write an equation for the conversion of (bromomethyl)benzene into (phenylnethyl)amine. Name the type of reaction taking place and explain why a low yield of product is obtained.

Equation

Type of reaction ...............................................................................................

Explanation ......................................................................................................

...........................................................................................................................

...........................................................................................................................

(ii) Name the type of reaction involved in the conversion of benzenecarbonitrile into (phenylmethyl)amine. Write an equation for this reaction and suggest a suitable reagent or a combination of reagent and catalyst. Explain why this method of preparation gives a high yield of product.

Type of reaction. ................................................................................................

Equation

Reagent(s) ........................................................................................................

Explanation ......................................................................................................

...........................................................................................................................

...........................................................................................................................

(9)

(b) State which of the two amines, (phenylmethyl)amine and phenylamine, C6H5NH2, is the weaker base, and explain your choice.

Weaker base ...............................................................................................................

Explanation ................................................................................................................ (3)

(Total 12 marks)

15. Consider the following reaction sequence:

(a) (i) Give the reagents required to carry out Step 1 and write an equation for the formation of the inorganic reactive intermediate involved.

Reagents............................................................................................................

Equation for formation of inorganic reactive intermediate..............................

...........................................................................................................................

(ii) Name and outline the mechanism for the reaction between this intermediate and compound A.

Name of mechanism.........................................................................................

Mechanism

(7)

(b) Name the type of reaction taking place in Step 2 and suggest a suitable reagent or combination of reagents for this conversion.

Type of reaction..........................................................................................................

Reagent(s)................................................................................................................... (2)

2

2 2

2

33

3 33 3

3COCH COCH CH(OH)CH

Step 1 Step 2

Step 4

Step 3

NO

NH NO

NO

CH(OCOCH )CH CH(OCOCH )CH

A B

E D

C

(c) Suggest a derivative of ethanoic acid which could be used as a reagent for carrying out Step 3. Name and outline the mechanism for this reaction. You may use ROH to represent compound C in the mechanism.

Reagent........................................................................................................................

Name of mechanism....................................................................................................

Mechanism

(6)

(d) Name the type of reaction taking place in Step 4 and suggest a suitable reagent or combination of reagents for this conversion.

Reagent........................................................................................................................

Name of mechanism.................................................................................................... (2)

(e) What type of stereoisomerism is shown by compound E?

.................................................................................................................................. (1)

(Total 18 marks)

1. (a) (i) What feature of the ammonia molecule allows it to act as a base?

..........................................................................................................................

(ii) Explain why methylamine is a stronger base than ammonia.

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

(iii) Explain why phenylamine is a weaker base than ammonia.

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (5)

(b) (i) Write an equation for the hydrogenation of propanenitrile to form propylamine. Give an example of a suitable catalyst for this reaction.

Equation............................................................................................................

Catalyst..............................................................................................................

(ii) Name the mechanism involved when propylamine is made from 1-bromopropane and ammonia.

..........................................................................................................................

(iii) Explain why the propylamine obtained in part (b)(ii) is not the only organic product formed.

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (5)

(c) Give the structure of the nitrogen-containing compound formed in the reaction between propylamine and ethanoic anhydride.

(1)

(d) The secondary amine CH3(CH2)11NHCH3 can be converted into a cationic surfactant by reaction with an excess of chloromethane. Name the type of product formed and give the structural formula of the compound.

Type of product...........................................................................................................

Structural formula

(3)

(Total 14 marks)

17. (a) Explain why phenylamine. C6H5NH2. is a weaker base than cyclohexylamine, C6H11NH2.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (3)

(b) Write an equation for the formation of cyclohexylamine from bromocyclohexane and an excess of ammonia. Name and outline the mechanism of this reaction.

Equation

Name of mechanism ...................................................................................................

Mechanism

(6)

(c) (i) Give the reagent used to convert bromocyclohexane into cyanocyclohexane, C6H11CN.

............................................................................................................................

(ii) Suggest a suitable reagent or combination of reagents for converting cyanocyclohexane into C6H11CH2NH2. Name the type of reaction involved and write an equation for the conversion.

Reagent(s) .........................................................................................................

Type of reaction ................................................................................................

Equation ............................................................................................................

............................................................................................................................

(4)

(d) Write an equation for the reaction between an excess of cyclohexylamine and ethanoyl chloride. Name and outline the mechanism for this reaction. You may use RNH2 to represent cyclohexylamine.

Equation .....................................................................................................................

....................................................................................................................................

Name of mechanism ..................................................................................................

Mechanism

(7)

(Total 20 marks)

3.3.12 Polymers

Understand how condensation polymers are formed

The repeating units in polyesters and polyamides and the linkages between them

Typical uses of these polymers

Draw the: repeating unit from a monomers structure; repeating unit from a section of the polymer chain and the structure of the monomer from a section of the polymer

Explain the nature of the intermolecular forces between molecules of condensation polymers

Explain why polyesters and polyamides can be hydrolysed but polyalkenes cannot

Polyalkenes are non-biodegradable whereas polyesters and polyamides are biodegradable

Describe the advantages and disadvantages of different methods of disposal of polymers, including recycling

3.3.13 Amino acids Draw the structures of amino acids as zwitterions and the ions formed from amino acids in acid or alkaline solution

Draw the structure of a peptide formed from up to three amino acids

Draw the structure of the amino acids formed by hydrolysis of a peptide

Identify primary, secondary and tertiary structures in diagrams

Explain how these structures are maintained by hydrogen bonding and S-S bonds

Understand how amino acids can be separated and identified using thin-layer chromatography

Understand chromatograms can be developed using agents such as ninhydrin or ultraviolet light

Calculate Rf Values from chromatograms

Understand enzymes are proteins and act as catalysts, with a stereospecific active site that binds to a substrate

Understand the principle of a drug acting as an enzyme inhibitor by blocking the activie site; computers can help to design these drugs

Explain why a stereospecific active site can only bond to one enantiomeric form of a substrate or drug

Describe the structure of a nucleotide

Describe a single strand of DNA as a polymer of nucleotides linked by covalent bonds

Explain how hydrogen bonding between base pairs leads to two complementary strands of DNA arranged in a double helix Explain why the Pt(II) complex cisplatin prevents DNA replication and is therefore used as a cancer drug Explain why such drugs can have adverse effects and appreciate that society needs to assess the balance between the benefits and adverse affects of drugs

1. The amino acid alanine is shown below.

(a) A sample of alanine is dissolved in water.

(i) Draw the structure of the main alanine species present in this aqueous solution and give the name of this type of species.

Structure

Type of species .................................................................................

(ii) Draw the structure of the alanine species formed when an excess of hydrochloric acid is added to the solution.

(3)

(b) Alanine molecules may be reacted together to form a polypeptide. Give the repeating unit of this polypeptide and name the type of polymerisation involved in

its formation.

Repeating unit

Type of polymerisation ....................................................................... (2)

(c) The repeating unit of a polyalkene is shown below.

Give the name of the alkene which is used to form this polymer.

..................................................................................................................................... (1)

(Total 6 marks)

2. (a) The compound H2C=CHCN is used in the formation of acrylic polymers.

(i) Draw the repeating unit of the polymer formed from this compound.

(ii) Name the type of polymerisation involved in the formation of this polymer.

...........………………………………………………………………………….

(2)

(b) When the dipeptide shown below is heated under acidic conditions, a single amino acid is produced.

(i) Name this amino acid.

...........………………………………………………………………………….

C C

CH

CH CH CH

H

3

3

2 3

H N C C N C COOH

H H HO

CH CH CH CH

2

2 23 3

(ii) Draw the structure of the amino acid species present in the acidic solution.

(2)

(c) The repeating unit of a polyester is shown below.

(i) Deduce the empirical formula of the repeating unit of this polyester.

...........………………………………………………………………………….

(ii) Draw the structure of the acid which could be used in the preparation of this polyester and give the name of this acid.

Structure ……..……………………………………………………………….

Name ………………………………………………………………………….

(iii) Give one reason why the polyester is biodegradable.

...........………………………………………………………………………….

...........………………………………………………………………………….

(4) (Total 8 marks)

CH CH O C CH CH C O

O O

2 2 2 2

4. (a) The hydrocarbon M has the structure shown below.

(i) Name hydrocarbon M.

...........................................................................................................................

(ii) Draw the repeating unit of the polymer which can be formed from M. State the type of polymerisation occurring in this reaction.

Repeating unit

Type of polymerisation .....................................................................................

(iii) The reaction between M and benzene in the presence of HCl and AlCl3 is similar to the reaction between ethene and benzene under the same conditions. Name the type of mechanism involved and draw the structure of the major product formed in the reaction between M and benzene.

Name of mechanism ..........................................................................................

Major product

(iv) Draw a structural isomer of M which shows geometrical isomerism.

(6)

(b) Draw the repeating unit of the polymer formed by the reaction between butanedioic acid and hexane-1,6-diamine. State the type of polymerisation occurring in this reaction and give a name for the linkage between the monomer units in this polymer.

Repeating unit

3

3

2 2CH CH C CH

CH

Type of polymerisation ...............................................................................................

Name of linkage ..........................................................................................................

(4) (Total 10 marks)

5. (a) “Terylene” is a condensation polymer that can be formed from benzene-1,4-dicarboxylic acid and ethane-1,2-diol. Draw graphical formulae to represent:

(i) benzene-1,4-dicarboxylic acid;

(1)

(ii) ethane-1,2-diol;

(1)

(iii) the polymer “Terylene”.

(2)

(b) Give the name of the type of condensation polymer of which “Terylene” is an example.

..................................................................................................................................... (1)

(c) Outline the difference between the formation of an addition polymer and a condensation polymer.

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (2)

(d) Give the name of one addition polymer.

..................................................................................................................................... (1)

(Total 8 marks)

6. Ethylbenzene is made by the reaction shown below.

(a) Identify two other substances required as catalysts in this preparation.

Substance 1 ............................................................................................................

Substance 2 ............................................................................................................ (2)

(b) Write an equation for the reaction of these two substances with ethene to form the reactive intermediate involved in the formation of ethylbenzene.

................................................................................................................................ (1)

(c) Name and outline a mechanism for the reaction between this reactive intermediate and benzene.

Name of mechanism ................................................................................................

Mechanism

(4)

(d) Draw the structure of the product formed in a similar reaction between benzene and cyclohexene.

+ H C CHCH CH

2

2

2

3

(1)

(e) Ethylbenzene is used to make phenylethene which can be polymerised to form poly(phenylethene). Name this type of polymerisation and draw the structure of the repeating unit in the polymer.

Type of polymerisation ...........................................................................................

Repeating unit ........................................................................................................ (2)

(Total 10 marks)

7. (a) Synthetic polyamides are produced by the reaction of dicarboxylic acids with compounds such as H2N(CH2)6NH2

(i) Name the compound H2N(CH2)6NH2

.....................................................................................................................

(ii) Give the repeating unit in the polyamide nylon 6,6.

..................................................................................................................... (2)

(b) Synthetic polyamides have structures similar to those found in proteins.

(i) Draw the structure of 2-aminopropanoic acid.

(ii) Draw the organic product formed by the condensation of two molecules of 2-aminopropanoic acid.

(2)

(c) Compounds like H2N(CH2)6NH2 are also used to make ionic compounds such as X, shown below.

(i) X belongs to the same type of compound as (CH3)4N+Br– Name this type of compound.

.....................................................................................................................

(ii) State a reagent which could produce X from H2N(CH2)6NH2 and give a necessary condition to ensure that X is the major product.

Reagent ........................................................................................................

Condition .....................................................................................................

(iii) Name the mechanism involved in this reaction to form X.

..................................................................................................................... (4)

(Total 8 marks)

8. The polymer poly(chloroethene), commonly known as poly(vinyl chloride) or PVC, can be produced as follows:

(a) Using your knowledge of the reaction between bromine and ethene, name and outline a mechanism for Step 1.

Name of mechanism ..................................................................................................

Mechanism

(5)

CH CH

N N(CH ) CH 2BrH C

CH CH

3

3 3

3 3

+ –+2 36

Compound X

C C

H Cl

2 2 22

4 2 2 3

H H

H C C H Cl C H ClCH n

PVC

Step 1 Step 2 Step 3

Cl heat

(b) Write an equation for Step 2 showing clearly the structure of the organic product.

.......................................................…….......................................................................

(1)

(c) Plasticisers are often incorporated into polymers such as PVC. Name a type of compound used as a plasticiser.

.......................................................…….......................................................................

(1)

(d) (i) Draw the structure of the organic product of the reaction of C2H4C12 with an excess of warm aqueous sodium hydroxide.

(ii) Suggest why C2H3Cl, the organic product of Step 2, does not react with warm aqueous sodium hydroxide.

............................................................................................................................

............................................................................................................................

(3) (Total 10 marks)

9. This question concerns the chemistry of ethene and compounds derived from it. Consider the following statements and then answer the questions below.

• Ethene may be polymerised to form poly(ethene).

3.3.14 Organic synthesis Explain why chemists aim to design processes that do not require a solvent and that use non-hazadous starting materials Explain why chemists aim to design production methods with fewer steps that have a high percentage atom economy Use reactions in this specification to devise a synthesis, with up to four steps, for an organic compound

Q1. Synthetic dyes can be manufactured starting from compounds such as 4-nitrophenylamine.

A synthesis of 4-nitrophenylamine starting from phenylamine is shown below.

(a) An equation for formation of N-phenylethanamide in Step 1 of the synthesis is shown below.

2C6H5NH2 + CH3COCl → C6H5NHCOCH3 + C6H5NH3Cl N-phenylethanamide

(i) Calculate the % atom economy for the production of N-phenylethanamide (Mr = 135.0).

(ii) In a process where 10.0 kg of phenylamine are used, the yield of N-phenylethanamide obtained is 5.38 kg.

Calculate the percentage yield of N-phenylethanamide.

(iii) Comment on your answers to parts (i) and (ii) with reference to the commercial viability of the process.

(7)

Q2. Compound W can be formed via compounds H and S in the three-step synthesis shown below.

Identify compounds H and S and give reagents and conditions for Steps 1 and 2.

State the type of compound of which W is an example.

W reacts with a large excess of bromomethane to form a solid product. Draw the structure of this product and name the type of mechanism for this reaction.

(Total 9 marks)

Q3. The following reaction scheme shows the formation of two amines, K and L, from methylbenzene.

(a) (i) Give the reagents needed to carry out Step 1. Write an equation for the formation from these reagents of the inorganic species which reacts with methylbenzene.

Reagents ............................................................................................

Equation .........….................................................................................

(ii) Name and outline a mechanism for the reaction between this inorganic species and methylbenzene.

Name of mechanism ............................................................................

Mechanism

Q4.This question refers to the reaction sequence below.

Which one of the following is not involved in the reaction sequence?

A esterification

B hydrolysis

C nucleophilic addition

D reduction (Total 1 mark)

Q5.This question concerns the preparation of the plastic poly(methyl 2-methylpropenoate) (Perspex), starting from propanone.

Which one of the following sets of reagents is not suitable for the step indicated?

A Step 1 HCN (NaCN then dilute HCl)

B Step 2 hot ethanolic KOH

C Step 3 warm aqueous H2SO4

D Step 4 CH3OH with an acid catalyst (Total 1 mark)

Q6. A possible synthesis of phenylethene (styrene) is outlined below.

(a) In Reaction 1, ethanoyl chloride and aluminium chloride are used to form a reactive species which then reacts with benzene. Write an equation to show the formation of the reactive species. Name and outline the mechanism by which this reactive species reacts with benzene.

(6)

(b) NaBH4 is a possible reagent for Reaction 2. Name and outline the mechanism for the reaction with NaBH4 in Reaction 2. Name the product of Reaction 2.

(6)

(c) Name the type of reaction involved in Reaction 3 and give a reagent for the reaction.

(2) (Total 14 marks)

Q7.Which one of the following pairs reacts to form an organic product with only 2 singlets in its proton n.m.r. spectrum?

A ethene and bromine

B propan-2-ol and acidified potassium dichromate(VI)

C ethanol and concentrated sulphuric acid

D epoxyethane and water in the presence of dilute sulphuric acid (Total 1 mark)

Q8. (a) Describe how propanal, CH3CH2CHO, and propanone, CH3COCH3, can be distinguished using

(i) a chemical test and

(ii) the number of peaks in their proton n.m.r. spectra. (5)

(b) Compound Z can be produced by the reaction of compound X with compound Y as shown in the synthesis outlined below.

Identify compounds X and Y. For each of the three steps in the synthesis, name the type of reaction involved and give reagents and conditions. Equations are not required.

(10)

3.3.15 Nuclear magnetic resonance spectoscopy

Explain why tetramethylsilane (TMS) is a suitable substance to use as a standard

Understand NMR gives information about the position of 1H or 13C atoms in a molecule and that 13C NMR gives simpler spectra than 1H NMR Chemical shift depends on the molecular environment; the use of the δ scale for recording chemical shift

Describe how 1H NMR spectra are obtained

Use 1H NMR and 13C NMR spectra and chemical shift data to suggest possible structures/ part structures for molecules Use integration data from 1H NMR spectra to determine the relative numbers of equivalent protons in the molecule Use the n+1 rule to deduce the spin-spin splitting patterns of adjacent, non-equivalent protons in aliphatic compounds (doublet, triplet & quartet)

3.3.16 Chromatography Describe thin-layer chromatography

Describe column chromatography

Describe gas chromatography

Understand that separation depends on the balance between solubility in the moving phase and retention by the stationary phase

Understand the use of mass spectrometry to analyse the components separated by GC

Calculate Rf values from a chromatogram

Compare retention times and Rf values with standards to identify different substances

REQUIRED PRACTICAL 12: Separation of species by thin-layer chromatography

1. The following five isomers, P, Q, R, S and T, were investigated using test-tube reactions and also using n.m.r. spectroscopy.

(a) A simple test-tube reaction can be used to distinguish between isomers P and S.

Identify a reagent (or combination of reagents) you could use. State what you would observe when both isomers are tested separately with this reagent or combination of reagents.

(3)

(b) A simple test-tube reaction can be used to distinguish between isomer Q and all the other isomers.

Identify a reagent (or combination of reagents) you could use. State what you would observe when Q is tested with this reagent or combination of reagents.

(2)

(c) State which one of the isomers, P, Q, R, S and T, has the least number of peaks in its 1H n.m.r. spectrum. Give the number of peaks for this isomer.

(2)

(d) Write the molecular formula of the standard used in 13C n.m.r. spectroscopy. Give two reasons why this compound is used.

_ (3)

(e) Figure 1 and Figure 2 show the 13C n.m.r. spectra of two of the five isomers.

Figure 1 Figure 2

The structures of the five isomers are repeated to help you answer this question.

State which isomer produces the spectrum in Figure 1 and which isomer produces the spectrum in Figure 2.

Explain your answer.

You do not need to identify every peak in each spectrum. Use Table C on the Data Sheet to answer the question.

(5)

Q2. This question concerns isomers of C6H12O2 and how they can be distinguished using n.m.r. spectroscopy.

(a) The non-toxic, inert substance TMS is used as a standard in recording both 1H and 13C n.m.r. spectra.

(i) Give two other reasons why TMS is used as a standard in recording n.m.r. spectra.

Reason 1 ______________________________________________________

______________________________________________________________

Reason 2 ______________________________________________________

______________________________________________________________

(2)

(ii) Give the structural formula of TMS.

(1)

(b) The proton n.m.r. spectrum of compound P (C6H12O2) is represented in Figure 1.

Figure 1

The integration trace gave information about the five peaks as shown in Figure 2.

Figure 2

δ / ppm 3.8 3.5 2.6 2.2 1.2

Integration ratio 2 2 2 3 3

(i) Use Table 2 on the Data Sheet, Figure 1 and Figure 2 to deduce the structural fragment that leads to the peak at δ 2.2.

(1)

(ii) Use Table 2 on the Data Sheet, Figure 1 and Figure 2 to deduce the structural fragment that leads to the peaks at δ 3.5 and 1.2.

(1)

(iii) Use Table 2 on the Data Sheet, Figure 1 and Figure 2 to deduce the structural fragment that leads to the peaks at δ 3.8 and 2.6.

(1)

(iv) Deduce the structure of P.

(1)

(c) These questions are about different isomers of P (C6H12O2).

(i) Draw the structures of the two esters that both have only two peaks in their proton n.m.r. spectra. These peaks both have an integration ratio of 3:1.

Ester 1

Ester 2

(2)

(ii) Draw the structure of an optically active carboxylic acid with five peaks in its 13C n.m.r. spectrum.

(1)

(iii) Draw the structure of a cyclic compound that has only two peaks in its 13C n.m.r. spectrum and has no absorption for C = O in its infrared spectrum.

(1)

(Total 11 marks)

Q3. This question is about some isomers of C5H8O2

(a) Compound H is a cyclic ester that can be prepared as shown.

On the structure of H, two of the carbon atoms are labelled.

HOCH2CH2CH2CH2COCl

+ HCL

H

(i) Name and outline a mechanism for this reaction.

Use Table C on the Data Sheet to give the 13C n.m.r. δ value for the carbon atom labelled a and the δ value for the carbon atom labelled b.

(7)

Q4. Which one of the following does not have a singlet peak in its proton n.m.r. spectrum?

A butyl methanoate

B propyl ethanoate

C ethyl propanoate

C methyl butanoate (Total 1 mark)

Q5. (a) Ester X, CH3CH2COOCH3, can be produced by the reaction between

propanoyl chloride and methanol. Name X and outline a mechanism for this reaction. Name the mechanism involved.

(6)

(b) The proton n.m.r. spectrum of X is shown below together with that of an isomeric ester, Y. Deduce which of Spectrum 1 and Spectrum 2 is that obtained from X. Use Table 1 on the Data Sheet and the integration data on the spectra to help you to explain your deduction. Suggest a structure for Y.

(4)

6. The proton n.m.r. spectrum of compound X is shown below.

4.3

4.2

4.1

4.0

3.9

3.8

3.7

3.6

3.5

3.4

3.3

3.2

3.1

3.0

2.9

2.8

2.7

2.6

2.5

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

Chem

ical

shift

, /p

pmδ

Compound X, C7H12O3, contains both a ketone and an ester functional group. The measured integration trace for the peaks in the n.m.r. spectrum of X gives the ratio shown in the table below.

Chemical shift, δ/ppm 4.13 2.76 2.57 2.20 1.26

Integration ratio 0.8 0.8 0.8 1.2 1.2

Refer to the spectrum, the information given above and the data below the Periodic Table provided to answer the following questions.

(a) How many different types of proton are present in compound X?

............................................................................................................................... (1)

(b) What is the whole-number ratio of each type of proton in compound X?

............................................................................................................................... (1)

(c) Draw the part of the structure of X which can be deduced from the presence of the peak at δ2.20.

................................................................................................................................ (1)

(d) The peaks at δ4.13 and δ1.26 arise from the presence of an alkyl group. Identify the group and explain the splitting pattern.

Alkyl group .............................................................................................................

Explanation .............................................................................................................

.................................................................................................................................

................................................................................................................................. (3)

(e) Draw the part of the structure of X which can be deduced from the splitting of the peaks at δ2.76 and δ2.57.

................................................................................................................................. (1)

(f) Deduce the structure of compound X.

................................................................................................................................. (2)

(Total 9 marks)

7. Compound Q has the molecular formula C4H7ClO and does not produce misty fumes

when added to water.

(a) The infra-red spectrum of Q contains a major absorption at 1724 cm–1. Identify the bond responsible for this absorption.

..................................................................................................................................... (1)

(b) The mass spectrum of Q contains two molecular ion peaks at m/z = 106 and m/z = 108. It also has a major peak at m/z = 43.

(i) Suggest why there are two molecular ion peaks.

...........................................................................................................................

(ii) A fragment ion produced from Q has m/z = 43 and contains atoms of three different elements. Identify this fragment ion and write an equation showing its formation from the molecular ion of Q.

Fragment ion ....................................................................................................

Equation ........................................................................................................... (3)

(c) The proton n.m.r. spectrum of Q was recorded.

(i) Suggest a suitable solvent for use in recording this spectrum of Q.

...........................................................................................................................

(ii) Give the formula of the standard reference compound used in recording proton n.m.r. spectra.

...........................................................................................................................

(2)

(d) The proton n.m.r. spectrum of Q shows three peaks. Complete the table below to show the number of adjacent, non-equivalent protons responsible for the splitting pattern.

Peak 1 Peak 2 Peak 3

Integration value 3 3 1

Splitting pattern doublet singlet quartet

Number of adjacent, non-equivalent protons

1

(1)

(e) Using the information in parts (a), (b) and (d), deduce the structure of compound Q.

(1)

(f) A structural isomer of Q reacts with cold water to produce misty fumes. Suggest a structure for this isomer.

(1)

(Total 9 marks)

Q8. Cyclohexene (boiling point = 83 °C) can be prepared by the dehydration of cyclohexanol (boiling point = 161 °C) using concentrated phosphoric acid.

A student prepared cyclohexene by placing 10 cm3 of cyclohexanol (density = 0.96 g cm–3) into a round-bottomed flask. 3 cm3 of concentrated phosphoric acid were then carefully added to the flask. The student added a few anti-bumping granules and set up the apparatus shown in the diagram.

• The student heated the mixture and collected the liquid that distilled at temperatures below 100 °C

• The distillate was poured into a separating funnel and washed by shaking with sodium carbonate solution.

• Periodically, the separating funnel was inverted and the tap opened. • The aqueous layer was discarded and the final organic product was dried

using anhydrous calcium chloride. • After the product was dried, the drying agent was removed by filtration

under reduced pressure.

(a) The student collected 5.97 g of cyclohexene in the experiment.

Calculate the percentage yield of cyclohexene. (3)

(b) Describe a test-tube reaction, on the product, to show that the cyclohexanol had been dehydrated.

State what you would observe. (2)

(c) Suggest why sodium carbonate solution was used to wash the distillate. (1)

(d) Explain why it is important to open the tap of the separating funnel periodically.

(1)

(e) Give a property of anhydrous calcium chloride, other than its ability to absorb water, that makes it suitable as a drying agent in this preparation.

(1)

(f) Describe the apparatus used to remove the drying agent by filtration under reduced pressure. Your description of the apparatus can be either a labelled diagram or a description in words.

(2)

(g) A sample of cyclohexene has been contaminated with cyclohexanol. The cyclohexene can be separated from the cyclohexanol by column chromatography. Silica gel is used as the stationary phase and hexane as the mobile phase.

Explain why cyclohexene has a shorter retention time than cyclohexanol. (2)

(h) Explain how an infrared spectrum would confirm that the cyclohexene obtained from the chromatography column did not contain any cyclohexanol.

(1) (Total 13 marks)

Q9. Chromatography is used to identify amino acid sequences in compounds.

The dipeptide cysteine-aspartic acid (cys-asp), J, and the dipeptide aspartic acid-cysteine (asp-cys), K, are shown.

(a) A mixture of the two dipeptides J and K is analysed by gas chromatography followed by mass spectrometry (GC-MS).

Explain why J and K can be separated by gas chromatography and why mass spectrometry using electrospray ionisation does not enable you to identify them.

(4)

(b) A tripeptide, L, is partially hydrolysed with concentrated hydrochloric acid to produce two dipeptides and the amino acids alanine (ala), lysine (lys) and serine (ser).

The two dipeptides are separated by chromatography. The diagram below shows the chromatogram.

The table below contains the Rf values of some dipeptides.

Dipeptide ala-lys ala-ser lys-ser lys-ala ser-ala ser-lys

Rf value 0.55 0.85 0.10 0.20 0.15 0.45

Use the chromatogram in the diagram above and the Rf values in the table to identify the two dipeptides present in spots M and N.

Use your answers to deduce the order of the amino acids in the tripeptide L.

(3) (Total 7 marks)

Q10. A peptide is hydrolysed to form a solution containing a mixture of amino acids. This mixture is then analysed by silica gel thin-layer chromatography (TLC) using a toxic solvent. The individual amino acids are identified from their Rf values.

Part of the practical procedure is given below.

1. Wearing plastic gloves to hold a TLC plate, draw a pencil line 1.5 cm from the bottom of the plate.

2. Use a capillary tube to apply a very small drop of the solution of amino acids to the mid-point of the pencil line.

3. Allow the spot to dry completely. 4. In the developing tank, add the developing solvent to a depth of not more

than 1 cm. 5. Place your TLC plate in the developing tank. 6. Allow the developing solvent to rise up the plate to the top. 7. Remove the plate and quickly mark the position of the solvent front with a

pencil. 8. Allow the plate to dry in a fume cupboard.

(a) Parts of the procedure are in bold text.

For each of these parts, consider whether it is essential and justify your answer.

(4)

(b) Outline the steps needed to locate the positions of the amino acids on the TLC plate and to determine their Rf values.

(4)

(c) Explain why different amino acids have different Rf values. (2)

(Total 10 marks)

Q11. (a) Because of the toxic nature of the copper(II) ion, a wide range of

alternative anti-fungal drugs has been developed for use in agriculture. One example is Zineb.

(i) The negative ion in Zineb could act as a bidentate ligand.

On the structure above, draw a ring around each of two atoms that could provide the lone pairs of electrons when this ion acts as a bidentate ligand.

(1)

(ii) Calculate the Mr of Zineb. Give your answer to the appropriate precision.

(1)

(iii) Name the functional group formed at each end of the negative ion when all the sulfur atoms in the structure of Zineb are replaced by oxygen atoms.

(1)

(b) Zineb has been investigated for harmful effects. Generally, Zineb has been found to be safe to use in agriculture. It is only slightly soluble in water and is sprayed onto plants. A breakdown product of Zineb is ethylene thiourea (ETU), which is very soluble in water. The structure of ETU is shown below.

Determine the percentage, by mass, of sulfur in ETU (Mr = 102.1). (1)

(c) Chromatography is a technique used to show the presence of a small amount of ETU in Zineb.

Outline how this technique is used to separate and identify ETU from a sample of Zineb powder.

(4) (Total 8 marks)

Q12. (a) A chemist discovered four unlabelled bottles of liquid, each of which

contained a different pure organic compound. The compounds were known to be propan-1-ol, propanal, propanoic acid and 1-chloropropane.

Describe four different test-tube reactions, one for each compound, that could be used to identify the four organic compounds. Your answer should include the name of the organic compound, the reagent(s) used and the expected observation for each test.

(8)

(b) A fifth bottle was discovered labelled propan-2-ol. The chemist showed, using infrared spectroscopy, that the propan-2-ol was contaminated with propanone.

The chemist separated the two compounds using column chromatography. The column contained silica gel, a polar stationary phase.

The contaminated propan-2-ol was dissolved in hexane and poured into the column. Pure hexane was added slowly to the top of the column. Samples of the eluent (the solution leaving the bottom of the column) were collected.

• Suggest the chemical process that would cause a sample of propan-2-ol to become contaminated with propanone.

• State how the infrared spectrum showed the presence of propanone.

• Suggest why propanone was present in samples of the eluent collected first (those with shorter retention times), whereas samples containing propan-2-ol were collected later.

(4)