91Ó°ÊÓ

Aldehydes and ketones undergo nucleophilic addition with two equivalents of alcohols to give acetals or ketals respectively.

Nucleophilic addition of alcohol to the carbonyl group begins with, first, the generation of hemiacetal, then in presence of an acid, the reaction proceeds. Then the protonation of the OH group, followed by loss of water occurs leading to the generation of an oxonium ion.

The steps involved in general are-

• Protonation of the carbonyl.
• Nucleophilic attack by the alcohol
• Deprotonation to form a hemiacetal
• Protonation of the alcohol
• Removal of water
• Nucleophilic attack of the nucleophile
• Deprotonation by water

Nucleophilic Addition of ortho cresol to acetone

Nucleophilic Addition of ethylene glycol to 2-pentanone

Since cyclic ketal cannot be formed, trans-cyclohexane-1,2-diol does not undergo nucleophilic addition with ketone.

Nucleophilic Addition of Trans cyclohexane 1,2-diol to Acetone

Nucleophilic Addition of cyclohex-2-ene-1-one to methyl alcohol

In all the reactions given above, the mechanism follows the same set of steps starting from the protonation of the carbonyl, to deprotonation by water.