Q21P - Organic Chemistry (Mcmurry)

Question

Treatment of 2-cyclohexenone with HCN/KCN yields a saturated keto nitrile rather than an unsaturated cyanohydrin. Show the structure of the product,

and propose a mechanism for the reaction.

Step-by-Step Solution

Answer

Step 1: Conjugate addition

Conjugate addition of a nucleophile in alpha,beta-unsaturated carbonyl compounds; ketone and aldehyde, happen in two ways:

• 1-2 conjugate addition
• 1,4 conjugate addition

In the Conjugate addition of nucleophile on thealpha,beta-unsaturated carbonyl compounds reaction forms the “enolate intermediate,” which is resonance stabilized.

Step 2: Structure of Keto nitrile product

2-cyclohexanone undergoes conjugate nucleophile addition on its double bond, leading to the formation of resonance stabilized carbanion intermediate, which on protonation forms the keto nitrile that is the 3-oxocyclohexanecarbonitrile product.

 

 

The formation and structure of keto nitrile product (3-oxocyclohexanecarbonitrile) are shown as follows:

                                       Formation of 3-oxocyclohexanecarbonitrile