3.7 Optical Isomerism

Question 1

What property must a carbon atom have for the molecule to display optical isomerism about that carbon atom?

Answer 1

4 different substituents attached to one carbon atom

Question 2

What are the similarities and differences between two optical isomers?

Answer 2

Same atoms and bonds, but they are non-superimposable mirror images of one another. NOT IDENTICAL in chemical properties necessarily.

Differ in the way they rotate plane polarised light- rotate plane of polarisation by the same angle but in different directions.

Question 3

What word is used to describe optically active molecules?

Answer 3

chiral

Question 4

What are the pair of isomers called?

Answer 4

Enantiomers

Question 5

What is the chiral centre?

Answer 5

The carbon that has four different substituents attached to it

Question 6

How is the chiral centre denoted?

Answer 6

C*

Question 7

How is light polarised?

Answer 7

By passing it through a polaroid filter, so oscillations are only in one plane.

Question 8

What is a structural isomer?

Answer 8

Same molecular formula different structures.

Question 9

What can structural isomers arise from?

Answer 9

Chain isomers
Position isomers
Functional group isomers

Question 10

What is a Functional group isomer?

Answer 10

Compounds with the same molecular formula but with atoms arranged to give different functional groups.

Question 11

What is a stereoisomer?

Answer 11

Same structural formulae but have a different spatial arrangement of atoms

Question 12

What are the two types of stereoisomers?

Answer 12

E-Z isomers and Optical isomers

Question 13

What is a chiral (asymmetric) carbon?

Answer 13

A carbon that has four different groups attached

Question 14

A chiral carbon has four groups arranged tetrahedrally around it, what does this cause?

Answer 14

Cause two different isomers that are not superimposable to be formed, which are mirror images.

Question 15

What are two compounds that are optical isomers of each other called?

Answer 15

enatiomers

Question 16

What is a racemic mixture?

Answer 16

A mixture containing (50/50) mixture of two isomers (enantiomers).

Question 17

Page 5 3.7 chem sheets

Question 17

How does a racemic mixture react with plane polarised light?

Answer 17

A racemic mixture will not rotate plane polarised light.

Question 18

How do optical isomers react with plane polarised light?

Answer 18

Optical isomers have similar physical and chemical properties, but they rotate with plane polarised light in different directions.

One enantiomer rotates it in one direction and the other enantiomer rotates by the same amount in the opposite direction. clockwise and anti-clockwise.

Question 19

How is racemate formed?

Answer 19

A racemate will be formed in a reaction mechanism when a reactant or intermediate has a trigonal planar group in the molecule is approached from both sides by an attacking species.