What type of reaction occurs when 1-(1-methylcyclopentyl)ethanone and 2,2-dimethylpropanal are combined in the presence of sodium hydroxide?

The correct choice is the aldol condensation, which is a reaction where two carbonyl compounds, typically aldehydes or ketones, react in the presence of a base to form β-hydroxy carbonyl compounds (aldol products). In this case, 1-(1-methylcyclopentyl)ethanone is a ketone and 2,2-dimethylpropanal is an aldehyde.

When these compounds are combined with sodium hydroxide, the base deprotonates one of the carbonyl compounds, generating an enolate ion. This enolate can then attack the carbonyl carbon of the other compound, forming a new C-C bond. After this initial step, the reaction undergoes a dehydration process where a molecule of water is eliminated, leading to the formation of an α,β-unsaturated carbonyl compound. This process is characteristic of aldol condensation reactions.

The presence of the base sodium hydroxide is critical as it promotes the formation of the enolate ion and facilitates the overall reaction mechanism, distinguishing it from other reaction types like elimination, addition, or substitution, which do not involve the same sequence of steps or intermediates. Thus, aldol condensation is the correct classification for the reaction occurring