Chem ch14

Worked solutions to student book questions Chapter 14 From organic molecules to medicines

Heinemann Chemistry 2 4th edition Enhanced Copyright Pearson Australia 2010 (a division of Pearson Australia Group Pty Ltd) 1

E1. List the ailments that can be treated by using acetylsalicylic acid (aspirin).

AE1. Aspirin is used as

analgesic or painkiller anti-inflammatory, reduces inflammation antipyretic, reduces fever anticoagulant, reduces blood clotting, prevention heart attack and stroke

Recent research suggests that aspirin can be used to prevent complications arising from diabetes and dementia and as a preventative to bowel cancer.

E2. Why should someone with stomach ulcers not take aspirin?

AE2. In the stomach COX-1 (cyclo-oxygenase-1) enzymes produce prostaglandins that protect the stomach lining. COX-2 enzymes are present at the site of an inflammation producing prostaglandins that promote inflammation resulting in pain and fever. Aspirin inhibits the production of both COX-1 and COX-2 enzymes. So while it can treat pain, fever and inflammation it can also cause stomach irritation by also inhibiting those prostaglandins that protect the stomach.

Q1. a Draw a flow chart showing the reaction pathways for the preparation of aspirin

from salicylic acid using: i ethanoic acid ii ethanoic anyhdride

b Explain why the pathway using ethanoic anhydride is preferred over the one using ethanoic acid.

c Which pathway could be considered greener because it produces the least amount of waste?

A1.

a i



ii

b The rate and yield is greater using ethanoic anhydride. c A green approach to chemical synthesis aims to maximise atom economy, the

number of reactants atoms incorporated into the desired product. The idea of atom economy was explained in Heinemann Chemistry 1, Chapter 17. Percentage atom economy is given by:

percentage atom economy = reactantsallofmassmolar

products in the used atoms of massmolar 100

For the reaction pathway using ethanoic acid, percentage atom economy

= 60138

180+

100

= 91.1% For ethanoic anhydride pathway, percentage atom economy

= 102138

180+

100

= 75% However, since the rate of reaction and the yield are greater using ethanoic anhydride, this is the preferred reaction.

Q3. Why do the instructions on prescription antibiotics tell you to complete the whole course of tablets?

A3. At the point when the symptoms of an infection disappear there may still be bacteria present in the body. If you cease taking antibiotics at this stage the bacteria may start multiplying again and the infection could return.

Q4.

Why were antibiotics like penicillin V preferred to penicillin G?

A4. Penicillin V is more stable in the presence of stomach acid so can be given to the patient in tablet form. Penicillin G is more potent but has to be given in the form of an injection, requiring a visit to a medical clinic.



Q5. What information about the molecular structure of a drug does each of these analytical techniques provide? a infrared spectroscopy b nuclear magnetic resonance spectroscopy c mass spectroscopy

A5. IR spectroscopy: Identity of any functional groups that may be present. Proton NMR: The number of hydrogen environments present in the molecule. Mass spectroscopy: Molar mass from the molecular ion; structure and identity from fragmentation pattern.

Q6. Medicinal proteins such as insulin are administered by injection. Suggest why they cannot be given orally as tablets or capsules.

A6. Since insulin is a proteinif it was given orally the substance would be broken down in the process of digestion before it could be absorbed.



Chapter review

Q7. Why is the sodium salt of acetylsalicylic acid more soluble than normal aspirin?

A7. Sodium acetylsalicylic acid is more soluble in water than acetylsalicylic acid because it dissociates into ions (Na+ and the acetylsalicylate anion) which then attract water molecules to form solvation sheaths around them.

Q8. Briefly explain how aspirin is able to reduce pain and fever.

A8. Aspirin blocks the action of the enzymes that control the production of prostaglandins substances that cause the blood vessels to constrict resulting in heat building up in the body to cause fever. Prostaglandins also make it easier for water to pass from blood capillaries into tissues where it causes swelling and pain.

Q9. Acetaminophen (paracetamol) is the active agent in some over-the-counter painkillers. It can be synthesised from p-hydroxyaniline (4-hydroxyaminobenzene) and acetic anhydride. An incomplete equation for this reaction is shown in Figure 14.25. a What by-product is formed in this reaction? b Determine the atom economy of this reaction.

A9. a ethanoic acid, CH3COOH. Note the similarity between this reaction and the

reaction for the synthesis of aspirin.

b Percentage atom economy = reactantsallofmassmolar

products in the used atoms of massmolar 100

= 102109

123+

100

= 58%

Q10. a The drugs celecoxib and rofecoxib were specifically designed to be COX-2

inhibitors. They do not affect the production of COX-1. Aspirin inhibits both COX-1 and COX-2. What are the benefits of these COX-2 inhibiting drugs over aspirin?

b Find out why rofecoxib, marketed as Vioxx, was withdrawn from use by the pharmaceutical company Merck.

A10. a The COX-2 inhibitors only works on the enzymes that are present at the site of

inflammation and not on those present in the stomach. Hence it does not cause stomach irritation or bleeding.



b Vioxx was withdrawn in 2004 because of concern that it has adverse side effects and may lead to the development of heart disease or stroke.

Q11.

From the description of the use of the Australian native plant with the Aboriginal name of bunaangu, what active ingredient might be present to give it these medicinal properties? You only eat the sap of the bunaangu. It has a bitter taste. You boil it up to drink. It helps toothache and a bad chest.

A11. From the description of the bitter taste of bunaangu and the symptoms that it helps to relieve, it seems as though the plant might be a source of salicin or possibly salicylic acid.

Q12.

As well as aspirin, analgesics include acetaminophen, ibuprofen, naproxen sodium, ketoprofen. Use the web to find out: a the names under which they are sold b their side effects c their chemical structure d how they are synthesised.

A12. The website Aspirin Adventures provides an easy to read summary of various pain killers. http://www.chemheritage.org/educationalservices/pharm/asp/asp00.htm

Q13. Codeine, morphine and heroin are drugs derived from the opium poppy. The molecular structure of these drugs is shown in Figure 14.26. Identify the part of each molecular structure that is common to all three drugs. How does the structure of these molecules differ?

Figure 14.26 Molecular structures of codeine, morphine and heroin. Cautionit is not possible to convert

codeine into morphine or heroin by any simple laboratory process.



A13. Different functional groups are attached to the benzene rings in each structure. Small changes to the molecular structure can result in significant changes to chemical or biochemical activity.

Q14. Suggest some advantages and disadvantages of using genetically modified plants to produce therapeutic proteins.

A14.

Advantages: convenient source of the medicinal protein that can be grown rather than produced via chemical synthesis. Could be included in the diet rather than having to be taken as a medication or could be used to supplement inadequate food supplies. Disadvantages: the effects of adding a medicinal protein to food has not been subjected to long-term studies. Also the modified gene may be transferred to other plants and result in unwanted harmful effects.

Q15. Use the web to find out about the diseases that are treated by the following medicinal proteins: a growth hormone b interferon c monoclonal antibodies

A15. a Growth hormone is used to treat children who fail to grow at a normal rate due to

growth hormone deficiency. b Interferon is used to treat hepatitis C. c Specific monoclonal antibodies can be used to treat certain types of cancer of the

kidney, leukaemia or lymphoma. Cytotoxic (cancer killing) substances are joined to the antibody and the resulting complex is given to the patient. The antibody, with the cytotoxic agent attached, then binds only to the cancer cells and eliminates them. Sometimes just the antibody itself is sufficient to trigger the bodys normal defence mechanism and stimulate it to eliminate the cancer cells.

Q16.

Illustrate, using aspirin as an example, how biochemists modify the structure of drugs to eliminate undesirable side effects.

A16.

Salicylic acid was used as a pain killer but found was to found to cause bleeding of the stomach walls. Its structure was modified by reaction salicylic acid (aspirin) with ethanoic acid to form the ester, acetylsalicylic acid which while an effective pain killer did not have this side effect. A soluble form of aspirin was developed by converting the carboxylic acid functional group to a sodium salt.



Q17. Explain why pharmaceutical companies manufacture drugs such as aspirin using chemical reactions, while biotechnological processes are used to produce drugs such as insulin.

A17. The active ingredients in drugs such as aspirin consist of organic molecules that can be made via a chemical pathway from some fairly simple feedstock. However, substances such as insulin are proteins that are made by the body. It would be very difficult to manufacture such a large molecule via a chemical pathway. Instead, they are made by adapting the structure of a related protein obtained from a biological source.



Unit 3 Area of Study 2 review

Multiple-choice questions

Q1. The smallest molecule in which homologous series must contain two carbon atoms? A an alkane B an alkanol C an alkene D an alkanoic acid

A1. C. There is a double bond between two carbon atoms in alkenes. The first members of the other homologous series, methane, methanol and methanoic acid all contain 1 carbon atom.

Q2. The systematic name for CH3CH2CH2CH(CH3)2 is: A 1,1-dimethylbutane B 2-methylpentane C 2-methylpentene D propyldimethylmethane

A2.

B. It may assist you to draw a full structural formula. This molecule is an alkane as there are no multiple bonds, therefore the name ends in ane There are 5 carbon atoms in the longest chain name must end in pentane. There is a methyl group on the second carbon atom from the end. This is represented as 2-methyl. The full name is 2-methylpentane.

Q3.

Which compound would be expected to have the highest boiling point? A CH3CH2CH2OH B CH3CH2CH2CH3 C CH3CH2CH2Cl D CH3CH2CH3

A3.

A. The alkanols have higher boiling points as the strength of the intermolecular forces are greater. The strength of hydrogen bonding in alkanols is greater than those in chloroalkanes. Only dispersion forces act between alkane molecules.



Q4. Which of the following statements are true of the homologous series of primary alkanols? I The members differ by one CH2 unit. II They are all strong bases. III They can be oxidised to form carboxylic acids. A I and II B II and III C I and III D I, II and III

A4.

C. Members of a homologous series differ by CH2. Alkanols can be oxidised to carboxylic acids by strong oxidants such as acidified permanganate or dichromate.

Q5. What is the product formed by the reaction of CH2CH2 with Br2? A CH2BrCH2Br B CH2CHBr C CH3CH2Br D CHBrCHBr

A5. A. Ethene, CH2CH2, will undergo an addition reaction with bromine. The double bond is broken and a bromine atom bonds to each carbon atom to form 1,2-dibromethane.

Q6. When ethanol is heated under reflux with an acidified solution of potassium dichromate (VI), the final product has the formula: A CH3CH2CH2OH B CH3COOCH3 C CH3COOH D CH3CH2CH3

A6. C. Ethanol is oxidised to ethanoic acid by an acidified potassium dichromate solution.

Q7. Consider the following reaction pathway:

ethene I chloroethane II ethanol III ethanoic acid The reactions that occur in steps I, II and III of the pathway are: A cracking, addition, hydrolysis B chlorination, substitution, addition C addition, hydrolysis, oxidation D addition, reduction, hydrolysis



A7. C. Ethene undergoes an addition reaction with HCl to form chloroethane. Chloroethane undergoes a hydrolysis reaction with water or NaOH to produce ethanol. Ethanol is oxidised to ethanoic acid by an acidified potassium dichromate solution.

Q8. Acetylsalicylic acid could be formed from salicylic acid by warming it with:

A ethanol B methanol C ethanoic acid D methanoic acid

A8.

C. The OH group on salicylic acid undergoes an esterification reaction with ethanoic acid to form acetylsalicylic acid (aspirin).

(Chemically inactive hydrogen atoms have been omitted for clarity.)



Q9. Consider the following molecular structures of substances that all function as drugs. (Chemically inactive hydrogen atoms have been omitted for clarity.)

The substances that are expected to have similar pharmaceutical effects are: A I and II B II and III C I and III D I, II and III

A9.

C. Compounds I and III have similar molecular structures and would be expected to have similar pharmacological effects.

Q10

The ester methyl ethanoate could be made by reacting together: A CH3CH2OH and CH3COOH B CH3CH2OH and HCOOH C CH3OH and CH3CH2COOH D CH3OH and CH3COOH

A10. D. Methyl ethanoate is formed by an esterification reaction between methanol, CH3OH and ethanoic acid, CH3COOH.



Q11. The correct systematic name for this substance is

A 2,4-dimethylhexane B 2-methyl-4-ethylpentane C 2-ethyl-4-methylpentane D 1,1,3-trimethylpentane

A11.

A. The substance is an alkane. The longest chain contains 6 carbon atoms. There are methyl side chains on the 2nd and 4th carbon atoms.

Q12. A carboxylic acid with five carbon atoms per molecule could have the formula: A C5H11COOH B CH3(CH2)4COOH C CH3CH2CH2CH2COOH D C3H7COOCH3

A12. C. The carboxylic acid having five carbon atoms is pentanoic acid.

Q13.

Which statement about compounds I and II is not true?

A The 13C NMR spectrum of compound I has three peaks, and that of compound II

has two peaks. B The low resolution 1H NMR spectrum of I has four peaks, and that of II has three

peaks. C The mass spectrum of both will show a peak at a mass-to-charge ratio of 60. D The fingerprint region of the IR spectra will be identical for both compounds.

A13. D. The compounds shown are propan-1-ol and propan-2-ol. They are isomers. The fingerprint region of the IR spectra of these compounds would be different as their structures are different.



Questions 14 and 15 refer to the following information. The following list gives the formulas of a number of important biochemical molecules.

C6H12O6 CO(NH2)2 C2H5NO2 C3H7NO2 I II III IV C17H33COOH C3H8O3 CO2 C17H35COOH V VI VII VIII

Q14. From the list, identify two molecules that would react together to form a dipeptide. A II and III B III and IV C IV and VI D IV and II

A14.

B. Amino acids undergo condensation reactions to form dipeptides; condensation polymerisation of amino acids produces proteins.

Q15. When a saturated fat undergoes hydrolysis, two products that might be formed are: A VI and VIII B I and III C V and VI D II and VIII

A15.

A. Fats hydrolyse to form fatty acids (V and VIII) and glycerol (VI); molecule VIII has only single C-to-C bonds in the hydrocarbon chain (CH3(CH2)16COOH) and is a saturated fatty acid, formed from a saturated fat.

Q16.

When starch is formed from glucose, the condensation reaction that occurs involves: A a carboxyl functional group and an amino functional group B two hydroxyl functional groups C a hydroxyl functional group and a carboxyl functional group D a hydroxyl functional group and an amino functional group.



A16. B. Carbohydrate molecules combine with one another because of condensation reactions between hydroxyl functional groups, OH. For example:

Q17.

Olive oil contains a high proportion of oils made from a fatty acid called oleic acid. The formula of oleic acid is C18H34O2. The number of carbon-to-carbon double covalent bonds in oleic acid is: A 0 B 1 C 2 D 3

A17. B. Oleic acid is CH3(CH2)7CH=CH(CH2)7COOH, i.e. there is one C-to-C double bond. When written in this format (C18H34O2) the saturated fatty acid has (2 18) = 36 H atoms, and this molecule has two fewer hydrogens, thus one double bond.

Q18. When a protein, such as insulin, is formed, the condensation reaction that occurs involves: A a carboxyl functional group and an amino functional group B two hydroxyl functional groups C a hydroxyl functional group and a carboxyl functional group D a hydroxyl functional group and an amino functional group.

A18. A. The amino group, NH2, of one amino acid reacts with the carboxyl functional group, COOH, of the other to form a peptide link, NHCO.



Q19. Protein molecules are formed by condensation reactions between amino acids. The secondary structure of many proteins is a helical shape. The type of chemical bond responsible for maintaining this shape is: A hydrogen bonds B iondipole bonds C ionic bonds D covalent bonds.

A19. A. Hydrogen bonds form between the positive dipole of an NH+ group in one peptide link of the protein and the negative dipole of a C=O group in another peptide link of the same protein molecule as shown in the diagram.



Short-answer questions

Q20. a What feature of the bonding of alkenes makes them so useful? b The presence of an alkene can be detected by shaking a sample with a dilute

aqueous solution of bromine. i Describe what changes you would observe if an alkene was present. ii Write a balanced equation for the reaction of aqueous bromine solution with

ethene. c i Give the name of an instrumental method that could be used to confirm that

the compound was an alkene. ii Outline briefly what observation would be expected in the output of the

method if the substance was an alkene. d Under suitable conditions chloroethene can be converted into a polymer.

i What type of polymerisation process would you expect chloroethene to undergo?

ii Write an unbalanced equation to represent the polymerisation reaction. iii Give the systematic name of the product.

A20. a Alkenes have a double covalent bond that allows them to make a range of useful

addition compounds. b i Brown bromine solution becomes colourless.

ii C2H4(g) + Br2(aq) CH2BrCH2Br(l) c i Infrared spectroscopy

ii Characteristic absorption of C=C bond at 2070 to 2250 cm1 d i addition polymerisation

ii n CH2CH2 ~[CH2CH2]n~ iii polyethene

Q21. a What is meant by the terms:

i renewable ii sustainable?

b Assume that petrol is made entirely of octane. i Write a balanced equation to represent the combustion of octane in an

abundant supply of air. ii Explain why the use of petrol as a fuel for vehicles is of environmental

concern. c The use of ethanol as an alternative biochemical fuel to petrol is increasing.

i Write a balanced equation for the combustion of ethanol in a good air supply. ii Why is the use of biofuel ethanol seen as being beneficial for the

environment?



A21. a i Resource is capable of being regenerated.

ii Resource is capable of meeting the demands of the user. b i 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(g)

ii The main product of the combustion of petrol in an internal combustion engine is carbon dioxide. Raised levels of carbon dioxide in the atmosphere are believed to be causing global warming, with all the undesirable climatic changes that could have severe impact on the entire world.

c i C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(g) ii Whilst combustion of ethanol produces carbon dioxide, the ethanol is made

from plant sources (biomass) and the plants have taken in atmospheric carbon dioxide by photosynthesis. Hence the use of ethanol as a fuel is not adding to the total amount of carbon dioxide in the atmosphere. An additional advantage is that the fuel burns more cleanly, causing less air pollution by particulate matter and oxides of nitrogen.

Q22. a Crude oil consists mainly of alkanes of varying molecular sizes. What feature of

the intermolecular forces of alkanes allows the alkanes to be separated into fractions at an oil refinery?

b Ethanol is an alternative biochemical fuel to petrol. i Draw the structural formula of ethanol. ii Why does ethanol have an affinity for water whilst the alkanes in petrol

do not? c E10 petrol contains 10% ethanol. Outline the environmental advantages using

E10 petrol.

A22. a The dispersion forces between the alkane molecules increase as the size of the

molecules increase. This leads to an increase in the boiling temperature. Hence the molecules can be separated in fractions (molecules of similar size) according to the temperature at which they liquefy.

b i

ii The hydroxyl functional group in ethanol is capable of hydrogen bonding to water. The alkane molecules in petrol do not possess this functional group (only held together by dispersion forces) so will not mix with water.

c E10 petrol contains 10% ethanol. The use of E10 reduces the amount of carbon dioxide put into the atmosphere from fossil fuel sources as the carbon atoms in the ethanol have come from plant sources. The plants in turn have obtained their carbon from current atmospheric carbon dioxide.



Q23. A student attempted to prepare a sample of acetylsalicylic acid (aspirin) starting from salicylic acid.

a Apart from salicylic acid (2-hydroxybenzoic acid), what other reagent is needed? b Write a balanced equation for the reaction. You may use either structural or

molecular formulas. c Salicylic acid and acetylsalicylic acid are both white crystalline solids. The

student collected and purified the product of the reaction before sending it off for analysis by proton NMR spectroscopy. How would the spectrum produced by this technique allow the student to identify whether or not any acetylsalicylic acid had been formed in the reaction?

d A sample of the product was also sent off for analysis by mass spectroscopy. In the spectrum returned there was a peak at m/e = 138 and a peak at m/e = 180. What does this tell you about the sample?

A23. a Ethanoic anhydride b

Alternative molecular formula equation: 2C7H6O3 + C4H6O3 2C9H8O4 + H2O

c 1H NMR spectrum would show a large peak at 2.2 ppm if the CH3 group was present, showing that acetylation had occurred.

d Peak at m/e = 138 is molecular ion peak of salicylic acid. Peak at m/e = 180 is molecular ion peak of acetylsalicylic acid. If both are present, the sample contains both reactant and product.



Q24. Traditional medicine used infusions of willow bark to help reduce pain and fever. Analysis has shown that the infusion contains the substance salicin. It is now known that digestive enzymes are able to convert salicin into salicylic acid. A student proposes to synthesise a soluble form of aspirin from salicin via the reaction pathway shown below.

a Name the type of reactions represented by the letters: A, B, C b Copy the two structures (salicin and salicylic acid) shown below and circle their

common features.

c Acetylsalicylic acid (aspirin) has the structure shown below:

i Circle the part of this molecular structure that would not contribute to its pharmaceutical activity.

ii Acetylsalicylic acid is hydrolysed to salicylic acid in the body. Explain why it is preferable to take acetylsalicylic acid rather than salicylic acid.



A24. a i A. Oxidation; the alkanol functional group is oxidised to the carboxylic acid

functional group ii B. Esterification reaction between the hydroxy functional group on salicylic

acid and ethanoic acid iii C. Acid base reaction between the COOH group and Na2CO3 or NaOH

b

c i

ii Acetylsalicylic acid does not have the acidic properties or unpleasant taste of

salicylic acid so can be taken much more easily and is much less irritating to the stomach. It does not hydrolyse back to salicylic acid until it reaches the small intestine.

Q25. Aspirin, acetylsalicylic acid, C9H8O4, is made by reacting salicylic acid, C7H6O3 (Mr = 138.0), with ethanoic anhydride, C4H6O3 (Mr = 102.0), according to the equation:

2C7H6O3 + C4H6O3 2C9H8O4 + H2O a Determine which is the limiting reagent if 10.0 g salicylic acid is reacted with

10.0 g ethanoic anhydride. b Find the maximum mass of acetylsalicylic acid that could be produced by this

reaction. c Explain why sufferers of pain and fever would prefer to take acetylsalicylic acid

(aspirin) rather than salicylic acid. Are there any situations where aspirin should not be given?



A25.

a n(salicylic acid) = 0.1380.10 = 0.07246 mol

n(ethanoic anhydride) = 0.1020.10 = 0.09804 mol

From the equation, 2 mol salicylic acid reacts with 1 mol ethanoic anhydride. Hence, 0.07246 mol salicylic acid reacts with 0.07246 mol ethanoic anhydride = 0.03623 mol ethanoic anhydride As there is 0.09804 mol ethanoic anhydride available, salicylic acid is the limiting reagent.

b From the equation, 2 mol salicylic acid forms 2 mol acetylsalicylic acid. Hence, 0.07246 mol salicylic acid forms 0.07246 mol acetylsalicylic acid. M(C9H8O4) = 180.0 g mol1 Maximum mass of acetylsalicylic acid = 0.07246 180.0

= 13.0 g (three significant figures) c Aspirin is preferred to salicylic acid as it does not have an unpleasant taste and

does not irritate the lining of the mouth and stomach. However, aspirin should not be given to children or adolescents suffering viral infections such as influenza or chickenpox as they can develop Reyes Syndrome (can be fatal). Also people who are taking prescribed amounts of aspirin as part of their treatment for other conditions should not take additional aspirin to counteract pain or fever. They should consult a pharmacist who will advise on appropriate action.

Q26. a Draw the structural formula for:

i hexanoic acid ii butan-2-ol iii pent-2-ene

b Draw the structural formula and provide the systematic name of four isomers of C4H9Cl.

c Give systematic names for: i CH3CH2CH2OH ii CH3CH2CH2COOH iii CH3CH2CH2COOCH2CH3



A26.

a i

ii

iii

b

b i propan-1-ol ii butanoic acid iii ethylbutanoate

Q27.

Ethyl hexanoate is an ester commonly used as artificial pineapple essence. a What starting materials are required to prepare a sample of this ester by one

reaction? b Describe the reaction conditions that you would use in this preparation. Explain

the purpose of any additional reagents. c Write a balanced equation to represent the reaction.



A27. a ethanol, hexanoic acid b Concentrated sulfuric acid is added as a catalyst. c CH3CH2OH(l) + CH3(CH2)4COOH)(l) CH3(CH2)4COOCH2CH3 (l)+ H2O(l)

Q28. The boxes below represent structures that make up a polymer of biological importance.

a What is the name of this biologically important polymer? b Draw a simple diagram using boxes to show the arrangement of the components

of a nucleotide containing cytosine. c Nucleotides can bond together to form a long chain. What name is given to this

type of reaction? What molecule is also produced in this reaction? d Draw a diagram to show the arrangement of nucleotide monomers in a single

strand of DNA. e Draw a simple diagram to show how two single polynucleotide strands are

aligned in DNA. Show any bonds that are formed between two single strands of DNA

f The structure of DNA is often described as a double helix. Explain what is meant by this term.

A28. a deoxyribonucleic acid, DNA b

c Condensation polymerisation, water



d

e

f Two strands of polynucleotides coiled around each other can be thought of as

similar in shape to a spiral staircase where the polynucleotides represent the handrails and the complementary base pairs are the steps.



Q29. a Explain how a DNA profile can be obtained. b How is a DNA profile used in forensic analysis?

A29.

a DNA is extracted from a sample of saliva, blood or tissue. Restriction enzymes are used to cut the DNA into fragments. The number of fragments are duplicated using polymerase chain reaction

(PCR). Fragments are sorted by length using gel electrophoresis. Radioactive or fluorescent probes are attached to the fragments. Bands are detected using X-ray film of light of various wavelengths.

b The profile obtained from a DNA sample is compared with the DNA profile obtained from a source whose identity is known. In criminal investigations, DNA profiles may be used to identify a suspect or remove an individual from suspicion. DNA profiling is also used to determine paternity and to identify victims of natural disasters.

Q30. Cysteine is an amino acid that forms part of the polypeptide chain in albumin, a protein that occurs in eggs. The Z-group of cysteine has the structure CH2SH. a Draw the structure of the amino acid cysteine. b On your diagram, label and name the two functional groups that are common to

all amino acids. c Draw the structure of cysteine at low pH. d Draw the structure of the two possible dipeptides that can form when a molecule

of cysteine reacts with a molecule of alanine (alanine has a Z-group of CH3).

A30.

a, b

c +NH3CH(CH2SH)COOH



d

Q31.

Condensation reactions are responsible for the formation of many important biomolecules, e.g. cellulose, proteins, starch, lipids. a Draw the structure of the products of the condensation reactions between the

following pairs of compounds: i

ii



iii

glycine serine

b Name the functional group that has been produced as a result of: i the reaction between glucose and fructose ii the reaction between glycerol and palmitic acid iii the reaction between glycine and serine

A31.

a i

ii

iii

b i glycoside link ii ester link iii peptide bond



Q32. Compound X contains hydrogen, carbon and oxygen. 4.50 g of X was burnt in excess air. 2.70 g of water was produced. 3.67 L of carbon dioxide measured at 25C and 1.00 atm pressure was also produced. a Determine the percentage composition of the compound. b What is the empirical formula of the compound? c The mass spectrum of compound X is shown below. Deduce the molecular

formula of X.

Mass spectrum of X.

d The molecular formula of compound X suggests that it is either a carboxylic acid or an ester. Write the structural formula and give the name of the two isomers that correspond to the molecular formula of X.

e Use the IR spectrum of X below to explain why the compound is not an acid.

IR spectrum of X.



f Explain why there are only two peaks in the 1H NMR spectrum of compound X shown below.

1H NMR spectrum of compund X.

g Identify compound X.

A32.

a n(H) = 182.70 2 = 0.3mol

m(H) = 0.3 1 = 0.3 g

%(H)= 4.50

100 0.3 = 6.67%

n(C) = RTpV =

29831.867.33.1011

= 0.15 mol

%C = 50.4

1001215.0 = 40.0%

%O = 100 (%H + %C) = 100 (6.67 + 40.0) = 53.33% b C : H : O % 40.0 : 6.67 : 53.33

n 12

0.40 : 0.167.6 :

1633.53

3.33 : 6.67 : 3.33 empirical formula = CH2O

c From the mass spectrum, the molecular ion has a m/e of 60, i.e. molecular mass is 60. The molar mass of CH2O unit is 30. There must be two CH2O units in the molecule. The molecular formula is C2H4O2.

d

e Refer to a table of IR absorptions. The IR spectrum of ethanoic would have a broad absorbance between 2500 cm1 and 3200 cm1 due the OH bond in



carboxylic acid functional group. Since this absorption is not present, the compound is not ethanoic acid.

f The two peaks represent two different hydrogen environments. The peak at chemical shift 8 is due to HCOO hydrogen and the peak at chemical shift of 3.7 is due to the three hydrogens in OCH3.

g methyl methanoate

Q33. The DNA profiles below were used as evidence in two separate court cases in which women (M) claimed particular men (F) were the fathers of their children (C).

a What do you think should have been the verdict in each case? b Each band in these profiles represents a repeating base sequence region. Why are

multiple repeating base sequence regions compared in DNA profiling?

A33.

a The DNA profile of the child in case 1 has a number of bands in common with that of the male. In this case, the male would be the father. In case 2, there are no common bands in the DNA profile of the child and the male. The male is not the childs father.

b The number of repeating base sequences in the non coding region of DNA vary between individual. In DNA profiling, the base sequences at 10 or more locations on the chromosomes are compared. Each individual (except identical twins) will have their own unique DNA profile.

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Chem ch14