Why do aldehydes undergo nucleophilic addition reactions while acyl chlorides undergo nucleophilic acyl substitution reactions? Once the nucleophile adds to the aldehyde, the tetrahedral intermediate is too sterically hindered to eliminate one of the attached groups. Because an Sw2 substitution can best take place on the sphybridized carborwyl carbon of the acyl halide. Once the nucleophile adds to the aldehyde, neither H” nor Rºcan function as a leaving group. so a substitution cannot take place. The carbonyl carbon of the aldehyde is more electrophilic than the carbonyl of the acyl chloride