Optical isomerism

• Write the equation for the reduction of butanone?

  Ch3Ch2COCh3 + 2[H] > Ch3Ch2Ch(OH)Ch3
• Explain why a product might have no effect on plane polarised light?

  Planar carbonyl group on product can be attacked from either side by the H-.

  Producing equal amounts of each enantiomer, existing in 2 chiral forms.

  With a racemic, the effects cancel out as it is rotated equally.
• What reaction is HCN and a carbonyl compound?

  Nucleophilic addition.

  
• How can you distinguish between 2 enantiomers?

  Use plane polarised light to rotate enantiomers in opposite directions.
• Why is a reaction using HCN very slow?

  As it is a weak acid, so very low amount of CN- ions.
• Why might plane polarised light not distinguish between 2 enantiomers?

  One enantiomer might be a racemate and inactive.

  One enantiomer might be achiral, therefore inactive.
• Why would a polymer be biodegradable?

  If it can be hydrolysed
• Define stereoisomers?

  Molecules with same structural formula, but different bond arrangement in space.
• Define racemic mixture and why it is formed?

  Equal mixture of enantiomers, formed from planar bond having equal probability of attack.
• Mechanism of aldehyde/ketone with KCN or KOH?

  Nucleophilic addition. Produces a nitrile/alcohol.

  
• what property must a carbon atom have for the molecule to display optical isomerism?

  4 dif substitutions attached
• how is light polarised?

  by passing it through a polaroid filter, so oscillations are only in one plane
• what affect does a racemate have on plane polarised light?

  none as the rotation by each enantiomer cancels out
• structure of a polarimeter?

  light source > polarising filter > polarised light passes through compartment containing sample > detector determines the angle of rotation of plane polarised light
• what are polarimeters used for?

  to identify which enantiomer is present, purity of sample, conc of sample
• why is optical isomerism an issue in the drug industry?

  sometimes only one enantiomer is effective due to enzymes active site being 3D
• how to resolve issue of only one enantiomer being effective?

  separate enantiomers

  sell racemate

  design alternative synthesis to only produce one enantiomer