Q19-5P - Organic Chemistry (Mcmurry)

Question

Treatment of an aldehyde or ketone with cyanide ion (${}^{-}\mathbf{:}\mathbf{C}\equiv \mathbf{N}$), followed by protonation of the tetrahedral alkoxide ion intermediate, gives a cyanohydrin.

Show the structure of the cyanohydrin obtained from cyclohexanone.

Step-by-Step Solution

Answer

Step-by-Step Solution Step 1:Formation of Cyanohydrin

Cyanohydrin formation occurs by adding “nucleophile cyanide (CN)” to the carbonyl carbon of aldehyde/ketone.

The formation of cyanohydrin leads to the following changes:

• The formation of an alkoxide ion intermediate by pushing an electron pair from the C=O bond to the oxygen atom.
• Carbonyl carbon hybridization change from ${\mathbf{sp}}^2\to {\mathbf{sp}}^3$ .

Step 2:Structure of Cyanohydrin formed

The nucleophile addition of cyanide ion on the carbonyl carbon of cyclohexanone (ketone) occurs in the following steps:

• Cyanide anion adds to the positively polarized carbon to form a tetrahedral intermediate.
• This intermediate is protonated to yield the cyanohydrin.

The formation and structure of the cyanohydrin are shown as follows:

Structure of cyanohydrin formed