3.3: Organic chemistry 2

Question 1

What is optical isomerism?

Answer 1

• molecules that are mirror images of each other (non-super imposable)
• never have all functional groups in the same place, not identical
• e.g. 2-aminopropanoic acid

Question 2

What type of molecules demonstrate optical isomerism?

Answer 2

• molecules with a chiral carbon
• chiral carbon- carbon atom bonded to 4 different functional groips
• same structural formula
• each isomer is known as an enantiomer (e.g. + or -/ D or L)

Question 3

How do you test for enantiomers?

Answer 3

• pass plane polarised light through a sample containing optical isomer
• depending on direction where plane of polarisation of planne polarised monochromatic light rotates we get:
  (+) enantiomer- rotates plane polarised light clockwise
  (-) enantiomer- rotates plane polarised light anti-clockwise

ALWAYS BY THE SAME AMOUNT

Question 4

What is a racemic mixture?

Answer 4

• a mixture with an equal amount of each enantiomer
• ‘optically inactive’ as doesn’t effect orientation of plane polarised light (cancel each other out)

Question 5

What is the mechanism to produce a racemate (racemic mixture)?

Answer 5

• nucleophillic substitution of cyanide in propanone