All the aldol reactions we discussed so far were between identical partners, meaning the same carbonyl compound served as an electrophile and a nucleophile in the form of an enolate:. Aldehydes or ketones lacking α-hydrogen atoms can possibly undergo self-oxidation and reduction reactions on heating with alkali (concentrated). SELF ALDOL CONDENSATION : When same type of aldehyde or ketone are react to give product is called self aldol condensation. Then this carbanion reacts with another carbonyl molecule to give the aldol product. These alpha hydrogen is acidic, therefore they are removed easily with bases (alkalis) and give carbanion. An aldol reaction between two different carbonyl compounds is called a crossed aldol or mixed aldol reaction. This test is Rated positive by 88% students preparing for Class 12.This MCQ test is related to Class 12 syllabus, prepared by Class 12 teachers. Nov 20,2020 - Test: Aldol Condensation | 27 Questions MCQ Test has questions of Class 12 preparation. Aldol condensation can be divided into two types 1. The nucleophile is generally an enolate of an aldehyde or ketone attacking another aldehyde or ketone molecule. Aldol condensation is occurred only in carbonyl compounds which have a alpha hydrogen.Carbonyl compounds are aldehydes and ketones. ii) Crossed Aldol reactions between an aldehyde and a ketone. To suppress this, along with the possible cannizzaro reaction, slow addition of acetaldehyde to benzaldehyde maintained in a mild alkaline medium is suggested. Moreover, cross aldol condensation reaction is also possible if one of the components in the reaction mixture is a ketone. Other Types of Reactions with α-Hydrogen Cannizzaro Reaction. Aldol condensation of aldehydes and ketones, mechanism. Note: In above reaction, the self aldol condensation of acetaldehyde is a competing reaction. Aldol condensation is a nucleophile attack on a carbonyl to make a ketone or aldehyde of β-hydroxy. Crossed aldol reaction is a variation of aldol reaction. aldol reaction: crossed aldol reaction: eg: Mechanism: Step 1: The hydroxide ion deprotanates the enolizable aldehyde reversibly. An acidic or basic solution can catalyze the condensation of aldol. Step 2: Enolate ion 1 preferentially adds to the non-enolizable aldehyde, which has the sterically less hindered and, therefore, more accessible carbonyl carbon.