Position IsomersPosition Isomers

Alkenes and alkanesAlkenes and alkanes

Use the models to find the isomers of Use the models to find the isomers of butene and butanebutene and butane

Draw them Draw them Name themName them Also identify the types of bonding in eachAlso identify the types of bonding in each How does the bonding affect the How does the bonding affect the

reactivity?reactivity? How can I tell the difference between How can I tell the difference between

cyclohexene and cyclohexane?cyclohexene and cyclohexane?

Alkenes and bromine waterIGCSE recallWhat is the product made when

ethene reacts with bromineUsing bromine water as a test Using bromine water as a test

for alkenesfor alkenes If you shake an alkene with bromine If you shake an alkene with bromine

water (or bubble a gaseous alkene water (or bubble a gaseous alkene through bromine water), the solution through bromine water), the solution becomes colourless. Alkenes becomes colourless. Alkenes decolourise bromine water.decolourise bromine water.

The chemistry of the testThe chemistry of the test This is complicated by the fact that the This is complicated by the fact that the

major product isn't 1,2-dibromoethane. major product isn't 1,2-dibromoethane. The water also gets involved in the The water also gets involved in the reaction, and most of the product is 2-reaction, and most of the product is 2-bromoethanol.bromoethanol.

However, there will still be some 1,2-However, there will still be some 1,2-dibromoethane formed, so at this sort of dibromoethane formed, so at this sort of level you can probably get away with level you can probably get away with quoting the simpler equation:quoting the simpler equation:

Draw the structure of : Draw the structure of : hex-2-enehex-2-enepent-2-enepent-2-eneWhy is it not possible to have pent-4-Why is it not possible to have pent-4-

ene?ene?Give the molecular formula of:Give the molecular formula of:pent-1-enepent-1-ene2,2-dimethylbutane2,2-dimethylbutane

Give the molecular and structural Give the molecular and structural formulae of the following:formulae of the following:

propanepropanepropenepropeneHow many chain isomers are How many chain isomers are

possible for:possible for:CC77HH1616

CC88HH1818

Stereo isomersStereo isomers Make but-2-ene with your modelsMake but-2-ene with your models Can you make any isomers of but-2-ene? Can you make any isomers of but-2-ene? Why is it possible with butene and not Why is it possible with butene and not

butanol?butanol?

The new E-Z naming systemThe new E-Z naming system Historically, alkenes have been named using cis- Historically, alkenes have been named using cis-

and trans- to represent stereochemistry around and trans- to represent stereochemistry around the double bond as you have just seenthe double bond as you have just seen

cis- for compounds where the "main substituents" cis- for compounds where the "main substituents" are on the same side of the double bond, and are on the same side of the double bond, and trans- when they are on opposite sides. trans- when they are on opposite sides.

This system clearly breaks down, however, in This system clearly breaks down, however, in more complex molecules where decisions more complex molecules where decisions concerning the "main substituents" are not easily concerning the "main substituents" are not easily made made

The E-Z system provides a set of rules to aid in The E-Z system provides a set of rules to aid in these decisions. You will see later that these these decisions. You will see later that these same rules are used in assigning priorities for same rules are used in assigning priorities for determining absolute configuration in chiral determining absolute configuration in chiral molecules. molecules.

Which is the main Which is the main constituents?constituents?

Which group get Which group get the priority?the priority?

The rules for assigning E-Z The rules for assigning E-Z designations are as follows:designations are as follows:

1.1. rank atoms directly attached to the double rank atoms directly attached to the double bond according to their bond according to their atomic numberatomic number

2.2. if there is a "tie" at any substituent, look at if there is a "tie" at any substituent, look at the second, third, etc., until a difference is the second, third, etc., until a difference is found found

3.3. multiple bonds count as multiple bonds count as multiplesmultiples of that of that same atom same atom

4.4. if the highest priority groups are on the if the highest priority groups are on the same sidesame side of the double bond, the of the double bond, the molecule is molecule is ZZ; if the highest priority groups ; if the highest priority groups are on are on opposite sidesopposite sides, the molecule is , the molecule is EE

Name this compoundName this compound

Name these… if you canName these… if you can

Organic Chemical Organic Chemical ReactionsReactions

Electrophilic AdditionElectrophilic Addition

Ethene reacts with Halogens or sulphuric Ethene reacts with Halogens or sulphuric acidacid

An electrophile is a positive (relative), An electrophile is a positive (relative), species that is attracted towards a species that is attracted towards a negative centrenegative centre

Which bond on ethene is a very negative Which bond on ethene is a very negative centre?centre?

Recall: Addition of bromine to ethene …Recall: Addition of bromine to ethene …the test for an alkenethe test for an alkene

Recall: Addition of steam to make alcoholsRecall: Addition of steam to make alcohols

Reactions of halogens with Reactions of halogens with etheneethene

What is the order of reactivity with the halogens? What is the order of reactivity with the halogens? CHCH22=CH=CH22 + X + X22 CH CH22X=CHX=CH22XX Write the equation for bromine and name the Write the equation for bromine and name the

productproduct BrBrδδ++-Br-Brδδ- - This is an induced dipole, now the This is an induced dipole, now the BrBrδδ++ is is

attracted to the attracted to the ππ (pi) bond (pi) bond This is the electrophileThis is the electrophile A more stable sigma bond forms and a bromine A more stable sigma bond forms and a bromine

ion is producedion is produced

There is a positive charge on the carbon There is a positive charge on the carbon without the bromine which then attracts without the bromine which then attracts the negative bromine ionthe negative bromine ion

HH22C=CHC=CH2 2 + + BrBrδδ++-Br-Brδδ- -

HH22CC++-CH-CH22Br + BrBr + Br- - BrBrHH22C-CHC-CH22BrBr

Result formation of dibromoethaneResult formation of dibromoethane

Hydrogen HalidesHydrogen Halides

The bond strength increases with increasing The bond strength increases with increasing electronegativityelectronegativity

Predict which will react the fastest HCl/HBr/HIPredict which will react the fastest HCl/HBr/HI This time the Hydrogen ion acts as the This time the Hydrogen ion acts as the

electrophile as the bond is Helectrophile as the bond is Hδδ++-Br-Brδδ- -

Hydrogen is the positive or electron deficient, Hydrogen is the positive or electron deficient, it goes by the same mechanism except there it goes by the same mechanism except there is a permanent dipole not induced which will is a permanent dipole not induced which will have what effect on the rate?have what effect on the rate?

There is a positive charge on the carbon There is a positive charge on the carbon without the bromine which then attracts without the bromine which then attracts the negative bromine ionthe negative bromine ion

HH33CHC=CHCHC=CH2 2 + + HHδδ++-Br-Brδδ- -

HH33CHCCHC++-CH-CH22HH + Br+ Br- - H H33CCBrBrC-CHC-CH22HH

Result formation of 2-bromopropaneResult formation of 2-bromopropane

Sulphuric acid catalysed Sulphuric acid catalysed reactions with ethenereactions with ethene

HH22C=CHC=CH2 2 + + δδ++H-OH-Oδδ--SOSO33H HH H22CC++-CH-CH22HH + HSO + HSO44--

HH33C-HC-H22CCδδ++-O -O δδ--SOSO33H + HH + H22O CHO CH33CHCH22OH + HOH + H22SOSO44

Why does the oxygen of water attack the Why does the oxygen of water attack the positive centre?positive centre?

HydrogenationHydrogenation

This is the catalytic addition of This is the catalytic addition of hydrogen to alkeneshydrogen to alkenes

What catalyst is used and what What catalyst is used and what other conditions are necessary?other conditions are necessary?

What industry uses this reactions?What industry uses this reactions? AnswersAnswers1.1. Nickel and 150Nickel and 150ooCC2.2. Food industry in the manufacture of Food industry in the manufacture of

margarinemargarine

Addition of oxidising agents to Addition of oxidising agents to alkenesalkenes

What is an oxidising agent?What is an oxidising agent?Name someName some If you add oxygen to an alkene what If you add oxygen to an alkene what

might you get?might you get?HH22C=CHC=CH2 2 + [O] = HO-H+ [O] = HO-H22CCHCCH22-OH-OHThis is called a diol as there are two This is called a diol as there are two

alchol groups attachedalchol groups attachedThis works with potassium manganate in This works with potassium manganate in

alkali and potassium dichromate in acidalkali and potassium dichromate in acid

PolymerisationPolymerisation

Names some plastics and derive the Names some plastics and derive the monomermonomer

Assign a use to these polymersAssign a use to these polymersWhat is the reaction mechanism for What is the reaction mechanism for

this reaction?this reaction?See if you can draw the repeating See if you can draw the repeating

unitunit

What are these What are these polymers and what polymers and what are their are their monomers?monomers?

Polymers Formula Method of manufacture Uses

Ethene C2H4 -[ C2H4]-n Addition (free radicals) Electrical insulation/plastic bags

Propene C3H6 -[ C2H3CH3 ]-n Addition (free radicals) Ropes and carpets

Chloro ethane C2H3Cl -[ C2H3Cl ]-n Addition (free radicals) Drain pipes and window frames

Tetrafluoro ethane C2F4 -[ C2F4]-n Addition (free radicals) Non-stick covering for frying pans clothing

Polyester (Terylene) See structures below Condensation Clothing/plastic bottles/ sails

Polyamides (Nylon) See structures below Condensation Clothing/ropes/fishing wire

These are the two monomers for These are the two monomers for the formation of Terylene the formation of Terylene

What are these molecules used What are these molecules used to make? to make? Hint- look at the joining bondsHint- look at the joining bonds

What is this polymer?What is this polymer?

Note that each monomer in both Note that each monomer in both teryleneterylene and and nylon nylon has has two two functional groupsfunctional groups –why would this be? –why would this be?

Benefits and drawbacks for Benefits and drawbacks for plasticsplastics

In you groups discuss the aboveIn you groups discuss the aboveWhat do the polymers you have looked What do the polymers you have looked

at remind you of when you look at the at remind you of when you look at the long chains?long chains?

What have they a lot of stored in their What have they a lot of stored in their bondsbonds

Why is it a good idea to recycle Why is it a good idea to recycle plastics?plastics?

What would you have to consider What would you have to consider when recycling them?when recycling them?

Optical isomersOptical isomers

What an optical isomer? What an optical isomer? Name the compoundName the compound Give the molecular Give the molecular

formulaformula Make the optical isomersMake the optical isomers Try to superimpose them Try to superimpose them

on top of one anotheron top of one another It is like trying to put your It is like trying to put your

left hand over your rightleft hand over your right