ORGANIC CHEMISTRY - optical isomers

Question 1

what property must C atom have to display optical isomerism about that C atom?

Answer 1

4 diff substituents attached to that one C atom

Question 2

similarities between 2 optical isomers?

Answer 2

• same atoms and bonds
• non-superimposable mirror images of each other
• rotate in polarised light at the same angle

Question 3

differences between 2 optical isomers?

Answer 3

• not identical in chemical properties necessarily
• differ in the way they rotate in polarised light
• rotate in polarised light in different directions
  D-isomer =rotate clockwise
  L-isomer = rotate anti-clockwise

Question 4

what word is used to describe optically active molecules?

Answer 4

chiral

Question 5

what are the pair of isomers called?

Answer 5

enantiomers

Question 6

what is the chiral centre?

Answer 6

the carbon which has 4 different substituents attached to it

Question 7

how is the chiral centre denoted?

Answer 7

C*

Question 8

how is light polarised?

Answer 8

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

Question 9

what effect does racemic mixture have on plane polarised light?

Answer 9

None, as the rotation by each enantiomer cancels out to nothing

Question 10

what effect does the + isomer have on plane polarised light?

Answer 10

rotates plane of polarisation clockwise

Question 11

what effect does the - isomer have on plane polarised light?

Answer 11

rotates plane of polarisation anticlockwise

Question 12

what is the structure of a polarimeter?

Answer 12

light source (unpolarised light) —-> polarising filter ( polarised light) —-> polarised light passes through compartment containing sample —-> detector determines angle of rotation and plane of polarised light

Question 13

what are polarimeters used for?

Answer 13

to identify which enantiomer is present, the purity of the sample, the conc of sample etc.

Question 14

draw the mechanism for nucleophilic addition?

Answer 14

draw

Question 15

why is optical isomerism a problem for the drug industry?

Answer 15

sometimes, only one enantiomer is effective due to enzymes active site

Question 16

what are the options to resolve the issue of one enantiomer being effective?

Answer 16

• separate enantiomers - difficult and expensive as have very similar properties
• sell racemate - wasteful as half is inactive
• design alternative synthesis to only produce on enantiomer.

Question 17

examples of optically active drugs?

Answer 17

ibuprofen, thalidomide