Question

Answer the following questions:
(i) Draw structure of the methyl hemiactetal of methanal.
(ii) There are two -NH$_2$ groups in semicarbazide. However, only one is involved in the formation of semicarbazones. Give reason.
(iii) How will you convert ethanol to 3-hydroxybutanal?

Hint:

For reactions involving aldehydes and alcohols, keep in mind their reactivity with nucleophiles and the common reactions they undergo.

Answer 1

(i) The methyl hemiactetal of methanal is structured as follows:
\[ \text{CH}_3\text{OH}_2\text{C=O} \longrightarrow \text{CH}_3\text{O}\text{CH}_2\text{OH} \]
(ii) Semicarbazide's semicarbazone formation involves only one -NH$_2$ group. The second -NH$_2$ group is sterically hindered and unreactive under standard conditions.
(iii) An aldol condensation converts ethanol to 3-hydroxybutanal through these steps:
- Ethanol is first oxidized to acetaldehyde.
- Acetaldehyde then undergoes condensation with another acetaldehyde molecule in a basic environment to yield 3-hydroxybutanal.