Concept:Reactions that cleave the carbon-oxygen (C-O) bond in alcohols (such as reaction with hydrogen halides, \(\text{S}_N1\) pathway) involve the formation of a carbocation intermediate.
Formula:$$ \text{R}_3\text{C-OH} \xrightarrow{\text{H}^+} \text{R}_3\text{C}^+ + \text{H}_2\text{O} $$
Solution:- The rate of reaction is directly proportional to the stability of the carbocation formed after water leaves.
- Alkyl groups donate electron density (hyperconjugation and inductive effect), stabilizing positive charge.
- A tertiary carbocation (three alkyl groups) is highly stable, whereas a primary carbocation is very unstable.
- Therefore, the reactivity order for C-O bond cleavage is Tertiary > Secondary > Primary.
Why other options are incorrect:Option C is the order of reactivity for reactions where the O-H bond breaks (acting as an acid), which is dictated by alkoxide stability, not carbocation stability.
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