Chapter 25 - Optical Isomerism

Question 1

define optical isomerism

Answer 1

a form of stereoisomerism where there are 4 groups bonded to a central atom, forming 2 molecules with non-superimposable mirror images of each other

Question 2

what are enantiomers

Answer 2

a pair of optical isomers which correspond to eachother

Question 3

whats a chiral carbon

Answer 3

the carbon with 4 different groups

Question 4

whats a racemic mixture or racemate

Answer 4

a 50/50 mixture of an enantiomer pair

Question 5

describe the optical effects of enantiomers

Answer 5

when polarized light is shone through a sample of enantiomers, one will rotate the plane of polarization in the clockwise direction and one in the anticlockwise direction
the + isomer is clockwise, the - isomer is anticlockwise

Question 6

why does a racemate have no optical effect on polarised light

Answer 6

because the effects of each isomer cancel out

Question 7

what is lactic acid

Answer 7

2-hydroxypropanoic acid

Question 8

what is stage one in the synthesis of lactic acid

Answer 8

ethanal undergoes nucleophilic addition with a CN group to form 2-hydroxypropanenitrile

Question 9

what is stage two in the synthesis of lactic acid

Answer 9

hydrolysis of 2-hydroxypropanenitrile with a mixture of water acidified with dilute HCl
the nitrile group is replaced with a carboxylic acid group.
the products are lactic acid and ammonium chloride