Question

Of the following, which is the product formed when cyclohexanone undergoes aldol condensation followed by heating?
A.
B.
C.
D.

Answer 1

Condensation between two molecules of an aldehyde or ketone to form a $\beta -$ hydroxy aldehyde or a $\beta -$ hydroxy ketone is called aldol condensation. It is possible only when the carbonyl compound contains at least one $\alpha -$ hydrogen atom.

Complete step by step answer:
Aldol condensation is a property of carbonyl compounds having hydrogen at $\alpha -$ carbon atom. Aldol means aldehyde and alcohol groups on the same molecule. It may occur between two aldehydes or ketones in the presence of a catalytic base. The reaction is only possible between two components having $\alpha -$ hydrogen.
When cyclohexanone undergoes aldol condensation in the presence of a base, it will produce a $\beta -$ hydroxy ketone.

The mechanism involves three steps:
-First is the acid-base reaction. Hydroxide functions as a base and removes the acidic $\alpha -$ hydrogen giving the reactive enolate.
-The nucleophilic enolate anion attacks the ketone at the electrophilic carbonyl carbon in a nucleophilic addition giving an intermediate alkoxide. Alkoxide ion is the conjugate base of alcohols.
-The alkoxide deprotonates a water molecule creating hydroxide and the aldol is formed.
-Addition of water results in the formation of condensation products.
-Water molecules are removed by heating in the presence of acid. This makes a double bond.
Thus the product formed is a $\alpha ,\beta -$ unsaturated alkene.
Hence the correct option is C.

Note:
Some conditions regarding the aldol condensation are:
A reversible equilibrium
${\text{OH}}$ is the base typically used in an aldol reaction.
Can be carried out either by aldehydes or ketones.
With aldehydes, the equilibrium favors products.
With ketones, the equilibrium favors the reactants.