Organic Chemistry II

Question 1

Optical isomers occurs …

Answer 1

when chiral , asymmetric

Question 2

Define Chiral

Answer 2

Has 4 different chemical groups attached to the central carbon

Question 3

Define Enantiomers

Answer 3

an isometric that has a non-superimposable mirror image

Question 4

Optical isomers have

Answer 4

two isomers - enantiomers due to its chiral centre

Question 5

Optical isomers have the same

Answer 5

chemical properties
Boiling points
Solubilities

Question 6

Optical isomers differ in the way

Answer 6

that they rotate plane polarised light in different lights

They have different biochemical reactions

Question 7

What is meant by polarised?

Answer 7

when light waves come out with peaks and troughs in a single plane

Question 8

Comment on Enantiomer rotation in a plane polarised monochromatic light .

Answer 8

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

Question 9

What is optical activity?

Answer 9

the ability of a single optical to rotate the plane of polarisation of plane polarised light in molecules containing a single chiral centre.

Question 10

what happens in a Racemic mixture?

Answer 10

There is no rotation as the plane polarised Light rotates in equally in opposite directions.

Question 11

What is a racemic mixture and its nature ?

Answer 11

A mixture containing an equimolar (50/50) amount of the two enantiomers. Hence does not rotate the plane of polarisation of plane polarised monochromatic light

Question 12

What does the angle through which the plane of polarisation is rotated depend on?

Answer 12

the nature of the enantiomer

The conc of the enantiomer in the solution

Question 13

Describe how optical activity is detected optically

Answer 13

Shine plane polarised light through the solution. If the plane of the polarised light is rotated there is optical activity.

Question 14

Formation of a racemate

Answer 14

A racemate will be formed when a trigonal planar reactant or intermediate is approached from both sides by an attacking species

Question 15

Give an example of reaction resulting in the formation of Nucleophilic Addition

Answer 15

Nucleophilic Addition of HCN to aldehydes or ketones ( unsymmetrical)

Question 16

Describe the formation of a race mate with SN1 mechanism

Answer 16

Halogen breaks away from the haloalkane forming a carbocation
Nucleophile ion can then attack from either sides - resulting in 2 enantiomers - race mate
No optical activity in products

Question 17

In the SN2 mechanism, would a race mate be formed?

Answer 17

no

Question 18

Describe what happens in the SN2 mechanism

Answer 18

In the SN2 mechanism no intermediates are formed and the reaction occurs via a transition state.
If the reactant was chiral then during the reaction the opposite enantiomer would form. The product will rotate light in the opposite direction to the reactant.

Question 19

What is another mechanism reaction which results in the formation of a racemate and how?

Answer 19

Electrophilic Addition of HBr to an unsymmetrical alkene