3.3.7 Optical isomerism

Question 1

Structural Isomer

Answer 1

Compounds with the same molecular formula but have a different arrangement of atoms
Functional - have different functional groups
Positional - functional groups attach to the main chain in a different place
Chain - the carbon atoms arranged branched

Question 2

Structure of acid anhydrides

Answer 2

r-c=o-0-c=o-r

Question 3

Structure of esters

Answer 3

r - c = o -o - r

Question 4

Stereo isomerism

Answer 4

EZ isomerism
Optical isomerism

Question 5

Optical isomerism

Answer 5

Two isomers that are non superimposable mirror images of each other - not identical
(most common tetrahedral)
Rotate plane polarised light in opposite directions
Have 3D structures

tetrahedral structure - (1 dash line, one wedge and 2 stright line)

Question 6

Chirality

Answer 6

marked by a *
One carbon that has 4 different groups attached to it

Question 7

Enantiomers

Answer 7

A pair of optical isomers

Question 8

Optical activity

Answer 8

Light vibrating electric and magnetic fields
polaroid - all vibrations cut except those in one plane

Question 9

Measuring optical rotation

Answer 9

Using a polarimeter
Polaried light passed through two solutions of the same concentration
One solution rotates the plane polarised light clockwise (pos isomer) - anticlockwise (neg isomer)

Question 10

Racemic mixture

Answer 10

Not optically active - effect is cancelled out
50:50 optically active isomers

Question 11

Example synthesis
(2-hydroxypropanoic acid)

Answer 11

Stage 1 - nucleophilic addition (CN-)
Doest favour one of the isomers CN- equal probability of attaching above or bellow
As the CH3CHO is planar
Makes racemic mixture
Stage 2 - hydrolysis reaction
nitrile converted to a carboxylic acid
Reacts with water - acidified with HCl

Question 12

Naturally occurring synthesis

Answer 12

Some reaction with a chiral centre - only one isomer is formed
As enzyme catalysts have specific active sites - meaning only one isomer is formed

Question 13

Optical isomers in the drug industry

Answer 13

Only one isomer needed - as fits with a receptor or enzyme
Methods to get one isomer
Separate the two isomer - difficult and expensive very similar properties
Sell mixture as a drug - wasteful half inactive (could be harmful)
Design an alternative synthesis route makes only one isomer

Question 14

Ibuprofen

Answer 14

Most made and sold as racemate