Cyanohydrins can be made from carbonyl compounds by generating CN- ions from HCN in the presence of a weak base.

In a similar reaction, -CH2CO2CH3 ions are generated from CH3CO2CH3 by strong bases.

Which compound can be made from an Aldehyde and CH3CO2CH3?

Option 1 : CH3CO2CH2CH(OH)CH3
Option 2 : CH3CH2CH(OH)CH2CO2CH3

The correct answer is Option 2. I understand why. But I do not understand why Option 1 is incorrect. Please help/advise me.

Option 1 is incorrect because it does not contain the -CH2CO2CH3 ion that is generated from CH3CO2CH3 by strong bases. The -CH2CO2CH3 ion is necessary for the reaction to occur, so Option 1 is not a valid product of the reaction.

Option 1, CH3CO2CH2CH(OH)CH3, is incorrect because it does not have the correct composition of atoms that would be formed in the reaction between an aldehyde and CH3CO2CH3.

In the reaction, -CH2CO2CH3 ions are generated from CH3CO2CH3 by strong bases. This means that the CH3CO2CH3 molecule is transformed into -CH2CO2CH3, where the hydrogen of the methyl group is replaced by a carbon atom.

In the case of Option 1, CH3CO2CH2CH(OH)CH3, the reaction would require the formation of -CH2CO2CH3 as mentioned above, but in addition, it also includes another molecule, CH3OH (methanol). This extra molecule is not formed in the reaction and is incorrect.

On the other hand, Option 2, CH3CH2CH(OH)CH2CO2CH3, correctly represents the compound that can be formed from an aldehyde and CH3CO2CH3. This compound includes the -CH2CO2CH3 functional group, which is generated from CH3CO2CH3, as well as an additional ethyl group.

To determine why Option 1 is incorrect, we need to understand the reaction mechanism involved in the formation of cyanohydrins using HCN and a weak base.

When an aldehyde reacts with HCN in the presence of a weak base, CN- ions are generated. These CN- ions attack the carbonyl carbon of the aldehyde, resulting in the formation of a cyanohydrin. The weak base provides the necessary conditions to facilitate the reaction by deprotonating the HCN to generate CN- ions.

Now, let's analyze Option 1 (CH3CO2CH2CH(OH)CH3). This compound appears to be a cyanohydrin as it contains the -OH group adjacent to the carbonyl carbon. However, it is important to note that in the given reaction, we are starting with an aldehyde, not a ketone (CH3CO2CH3). The formation of a cyanohydrin from an aldehyde requires the presence of HCN and a weak base, as mentioned earlier.

In Option 1, CH3CO2CH2CH(OH)CH3 is a diol or a gem-diol, not a cyanohydrin. It is formed through the addition of water (H2O) across the carbonyl group of an aldehyde under different reaction conditions, typically acidic conditions. This reaction is known as hydration or hydrate formation. The presence of the carboxylate group (-CO2CH3) in Option 1 indicates the involvement of acetic acid (CH3COOH) as a reactant, further supporting the hydration reaction.

Therefore, Option 1 cannot be formed from an aldehyde and CH3CO2CH3 in the given reaction conditions involving HCN and a weak base. The correct answer, Option 2 (CH3CH2CH(OH)CH2CO2CH3), represents the formation of a cyanohydrin from an aldehyde and CH3CO2CH3 using strong bases, as mentioned in the question.