Question

The correct order of reactivity of the following towards nucleophilic addition reactions is: \[ \text{I. CH}_3\text{COCH}_3,\quad \text{II. CH}_3\text{CH}_2\text{CHO},\quad \text{III. ClCH}_2\text{CHO} \]

• A. III<I<II
• B. III<II<I
• C. I<III<II
• D. I<II<III

Hint:

Electron-withdrawing groups (like Cl) increase the reactivity of carbonyl compounds toward nucleophilic addition.

Answer 1

The Correct Option is D

Nucleophilic addition reactions are favored by the presence of electron-withdrawing groups that increase the partial positive charge on the carbonyl carbon, making it more susceptible to nucleophilic attack. - Compound I (CH$_3$COCH$_3$) is a ketone and is less reactive due to electron-donating alkyl groups. - Compound II (CH$_3$CH$_2$CHO) is an aldehyde and more reactive than ketones. - Compound III (ClCH$_2$CHO) is an aldehyde with an electron-withdrawing chlorine atom, which enhances the electrophilicity of the carbonyl carbon further. Hence, the correct order is: \[ \text{CH}_3\text{COCH}_3<\text{CH}_3\text{CH}_2\text{CHO}<\text{ClCH}_2\text{CHO} \]

Answer 2

The correct order of reactivity of the following towards nucleophilic addition reactions is:

\[ \textbf{I. CH}_3\textbf{COCH}_3,\quad \textbf{II. CH}_3\textbf{CH}_2\textbf{CHO},\quad \textbf{III. ClCH}_2\textbf{CHO} \]

Step 1: Understand the nature of compounds:
- I. CH₃COCH₃ is a ketone (acetone).
- II. CH₃CH₂CHO is an aldehyde (propanal).
- III. ClCH₂CHO is an aldehyde with an electron-withdrawing group (Cl) on the α-carbon.

Step 2: Compare reactivity:
- Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to less steric hindrance and less electron-donating effect from surrounding groups.
- Electron-withdrawing groups (like Cl in compound III) increase the electrophilicity of the carbonyl carbon, enhancing reactivity.

Step 3: Apply this understanding to order the reactivity:
- CH₃COCH₃ (I) is least reactive (a ketone).
- CH₃CH₂CHO (II) is more reactive (an aldehyde).
- ClCH₂CHO (III) is most reactive (aldehyde with electron-withdrawing group).

Correct order:
\[ \boxed{\textbf{I < II < III}} \]