Question

what is the acetal formed in the reaction below, if two equivalents of alcohol are used?
h₃c—ch₂—c—ch₃ + h₃c—ch₂—ch₂—oh ⇌ h₂so₄

Explanation:

Step1: Recall acetal - formation reaction

The reaction of a ketone with two equivalents of an alcohol in the presence of an acid catalyst ($H_2SO_4$ here) forms an acetal. The carbon - oxygen double bond of the ketone is transformed.

Step2: Identify the reactants

The ketone is $H_3C - CH_2 - C(=O)-CH_3$ and the alcohol is $H_3C - CH_2 - CH_2 - OH$.

Step3: Determine the acetal structure

In the acetal formation, the carbonyl oxygen of the ketone is replaced by two alkoxy groups from the alcohol. The general formula for the acetal formed from a ketone $R_1 - C(=O)-R_2$ and an alcohol $R - OH$ is $R_1 - C(OR)_2 - R_2$. Here, $R_1=H_3C - CH_2$, $R_2 = CH_3$ and $R = CH_2 - CH_2 - CH_3$. The correct structure has two $-O - CH_2 - CH_2 - CH_3$ groups attached to the carbon that was part of the carbonyl group of the ketone.

Answer:

The third structure (from the top) where the central carbon has two $O - CH_2 - CH_2 - CH_3$ groups and is also bonded to $H_3C - CH_2$ and $CH_3$ groups.