Optical isomerism：练习题

Which of the following best defines the term enantiomers?

A solution containing a racemic mixture of an optically active compound is tested with plane-polarised light. Which of the following observations would be made?

Consider the reduction of the following carbonyl compounds using \( \text{NaBH}_4 \). Which reaction will produce a product that exists as a racemic mixture?

Which of the following compounds contains a chiral centre and can therefore exist as optical isomers?

When 2-chlorobutane reacts with warm aqueous sodium hydroxide, the product formed is butan-2-ol. If the reaction proceeds via an \( \text{S}_{\text{N}}1 \) mechanism, a racemic mixture is produced. What is the reason for this?

Define the term chiral centre as applied to an organic molecule.

Identify the position of the asymmetric carbon atom in 2-hydroxypropanenitrile and list the four different functional groups or atoms attached to it.

When but-1-ene reacts with \( \text{HBr} \), the product 2-bromobutane is formed as a racemic mixture. Explain this observation by referring to the geometry of the intermediate formed during the reaction.

The molecule butan-2-ol exhibits optical isomerism.
a) Explain what is meant by an asymmetric carbon atom. (1 point)
b) Identify the chiral centre in butan-2-ol by providing the number of the carbon atom in the chain, assuming the principal functional group is on the lowest possible number. (1 point)
c) State the specific term used for the two non-superimposable mirror-image forms of butan-2-ol. (1 point)
d) Name the piece of equipment used to distinguish between these two isomers. (1 point)

Propanal reacts with hydrogen cyanide to form 2-hydroxybutanenitrile.
a) Draw the skeletal formula of 2-hydroxybutanenitrile and mark the chiral centre with an asterisk (*). (2 points)
b) Explain why the organic product is formed as a racemic mixture. In your answer, refer to the geometry of the propanal molecule and the nature of the nucleophilic attack. (3 points)