Aldehydes and Ketones

Question 1

Describe the shape of aldehydes and ketones

Answer 1

Trigonal planar

Question 2

Mechanism for the addition of NaBH₄ (reducing agent) (same with cyanide- :CN-)

Answer 2

1) Arrow from :H⁻ to C
2) Arrow from double bond to O
3) Arrow from :O to H⁺ (forms OH bond)

Question 3

What molecules give rise to stereoisomerism?

Answer 3

Compounds that contain an asymmetric carbon atom form stereoisomers that differ in their effect on plane polarised light.

Question 4

What gives rise to optical isomerism?

Answer 4

An asymmetric carbon atom is a chiral atom which gives rise to enantiomers. These exist as non super-imposable mirror images.

Question 5

What is the term for a mixture of equal amounts of enantiomers?

Answer 5

Racemic mixtures

Question 6

What does being planar mean for aldehydes and ketones?

Answer 6

They have an equal chance of being attacked above or below the plane of the molecule.

Question 7

What are enantiomers?

Answer 7

They rotate plane polarised light in opposite directions.

• They have very similar physical and chemical properties
• May have different biological properties