Chirality

Question 1

what is optical isomerism ?

Answer 1

a form of stereoisomerism - optical isomers: non - superimposable mirror images of each other

Question 2

what is required for optical isomerism to arise ?

Answer 2

1. chiral central ( carbon atom, sometimes nitrogen. with 4 different groups/ atoms attached to it )
2. mirror images are non superimposable
3. no internal plane of symmetry( due to chirality

Question 3

what are enantiomers ?

Answer 3

isomers that are mirror images of each other

Question 4

what are the properties of enantiomers are similar or different ?

Answer 4

• same physical properties
• similar chemical properties
• completely different biological properties

Question 5

what is plane polarized light ?

Answer 5

light that passes through a sheet of polaroid in a single direction

Question 6

how do optical isomers affect plane polarized light ?

Answer 6

• one optical isomer rotates plane polarized light anticlockwise whereas the other isomer rotates plane polarized light in a clockwise direction

Question 7

why can you react two a chiral things together and get a racemic mixture of a chiral product ?

Answer 7

• because when two molecules react, there is often an equal chance of forming each of the enantiomers
• e.g. with butane and chlorine, equal chance of each of the H atoms being replaced with the CI

Question 8

SN1 mechanism

Answer 8

2 steps
- first step is reversible, second step is not
- start with a single enantiomer reactant
- STEP 1 : a group breaks off, leaving a planar ion
- STEP2: planar ion can attacked from either side
- means the products will be racemic mixture of two optical isomers of each other
- so does not rotate plane polarized light as it cancels out

Question 9

SN2 mechanism

Answer 9

• only 1 step
• OH attaches and the CI leaves in the same step
• when OH attaches it flips “inverts” the chiral center - if an optically pure reactant is used then an optically pure product will be formed
  -produces chiral molecule ( polarizes light)