Unit 6: Synthesising Organic Compounds
Assignment 6.1
Isomerism in Organic Chemistry arises when molecular formulae are the same, but the arrangement of atoms is different.

Describing and explaining with examples, the different types of isomerism encountered in organic chemistry by focusing on:
a) Structural: including function group isomerism
Stereoisomerism: i.e. geometric and optical, with explanations of how this type of isomerism arises. You must use examples to explain.

Structural Isomerism
Structural isomers are atoms which are organised in different steps. The structural isomers tend to have the same atoms. There are types of structural isomers for example there is chain isomers which will occur only because the chances of the carbon chains which have a branch. For example butane C4H10 will consist of two isomers, there is a chain which is unbranched in the four carbon atom which is called butane. There is another branch which has three carbon atoms.

H H H H

H C C C C H H H H H

There is also the positioning of the isomerism where the essential carbon skeleton will stay the same but the groups that are considered as important move around on the skeleton form. For an example there is a position isomerism in C3H7BR there are two structural isomers, in an individual bromine atom the structural isomer is at the end of the chain but the other structural isomer is linked in the middle.

CH3 CH2 CH2 Br

The functional group isomerism will have different types of structural isomerism. The isomers will consist of different functional group which will belong to the other relatives of the compounds for example for C3H6O the functional group maybe an aldehyde known as propanol and the other is a ketone which is known as Propanone. O CH3
CH3 CH2 C H C O
This is propanol CH3 This is Propanone.
Stereoisomerism
Stereoisomerism are when the atoms start to making up the isomers which are attached up in the exact way, it will have space between each other. There are two types of stereoisomerism which is Geometric isomerism and Optical Isomerism.
Geometric isomerism
Geometric Isomers are also known as Cis-Trans Isomers. The Cis-Trans Isomers are seen when the rotation takes place around the chemical bond is unbearable. There are double and triple bonds seen. An example of the geometric isomers is But-2-ene (Trans) and (Cis) But-2-ene. The CH3 group is seen on the opposite side of the double bond but in different matters they will be on the same side.

H CH3 H H C C C C
CH3 H CH3 CH3

TRANS but-2-ene CIS But-2-ene

Optical Isomers
Optical Isomers are known as this due to the fact that they will have an effect on the plane polarised light. They are molecules which seem to have a mirror image of each other. Usually the mirror image molecules are known as enantiomer. The solution of an individual enantiomer will rotate the plane of the polarisation clockwise. These enantiomers are the (+) form for an example the individual optical isomers of an amino acid alanine goes by the name of (+)Alanine. The solution of the other optical isomers will be rotated to the plane of polarisation anti clockwise. The optical isomers is the (-) form for example Alanine is (-)Alanine. If the solution is concentrated equally, then the quantity of the rotation which is affected by the two isomers will be similar but in a symmetrical direction. When it will be optically active the substance will then be produced in the laboratory. This will usually arise as an equal mixture of the two optical isomers. The name of this is a racemic mixture. This will not have a result on the plane polarised light. The way that the optical isomers will occur is for an example the organic optical isomers which consist of a carbon atom that is attached to the four other sets. The chiral and achiral molecules will have an important difference. If there are two sets that seem to be similar that are linked