Question

The rate of solvolysis for the following tertiary halides in 80% aqueous ethanol at 25°C follows the order:

• A. \( I<II<III \)
• B. \( II<III<I \)
• C. \( III<II<I \)
• D. \( I<III<II \)

Hint:

When analyzing solvolysis reactions, focus on the stability of the carbocation intermediate. More stable carbocations, such as those with resonance stabilization or hyperconjugation, lead to faster reactions.

Answer 1

The Correct Option is B

The rate of solvolysis of tertiary halides depends primarily on the stability of the carbocation intermediate formed after the halide leaves. The more stable the carbocation, the faster the solvolysis rate. The stability of the carbocation is influenced by both inductive and resonance effects as well as the ability to relieve strain in cyclic structures. 
Let us analyze each compound: 
- For compound I (a simple alkyl tertiary halide), the carbocation formed after the halide leaves is relatively unstable since it only has the inductive stabilization from the surrounding alkyl groups. The solvolysis rate for I is slower compared to the others. 
- For compound II (a cyclic tertiary halide), the carbocation formed is more stable due to the ability of the ring to relieve strain upon carbocation formation. This makes the solvolysis faster than compound I. 
- For compound III (a tertiary halide with more alkyl groups), the resulting carbocation is highly stabilized due to both inductive effects from the alkyl groups and hyperconjugation. Therefore, compound III undergoes solvolysis faster than compound II and I. Thus, the correct order of the solvolysis rate is: 
\[ II<III<I \]