Rate of dehydration of alcohols follows the order:

The rate of dehydration of alcohols to form alkenes depends on the mechanism and the stability of the intermediate or transition state. Dehydration typically occurs via an acid-catalyzed elimination reaction (E1 or E2 mechanism), where the rate-determining step involves the formation of a carbocation for E1 or the stability of the transition state for E2.

First, recall the stability order of carbocations: tertiary (3°) carbocations are more stable than secondary (2°), which are more stable than primary (1°), and methyl carbocation (CH3+) is the least stable. This stability directly affects the rate in E1 mechanisms because the formation of a more stable carbocation is faster.

For tertiary alcohols (3°), dehydration proceeds via E1 mechanism, forming a stable tertiary carbocation, leading to a fast reaction. Secondary alcohols (2°) also undergo E1 but form a less stable secondary carbocation, so the rate is slower than tertiary but faster than primary. Primary alcohols (1°) usually undergo E2 mechanism because primary carbocations are highly unstable. In E2, the reaction rate depends on the stability of the transition state, which is influenced by the ability to remove a β-hydrogen. Primary alcohols have fewer electron-donating groups, making the transition state less stable, hence slower dehydration compared to secondary and tertiary.

Now, consider methanol (CH3OH). It is a primary alcohol but lacks a β-carbon and β-hydrogen. Without a β-hydrogen, intramolecular dehydration to form an alkene is impossible. Methanol can undergo intermolecular dehydration to form dimethyl ether under specific conditions, but this is not the same as alkene formation. Therefore, for alkene production, methanol has no rate or an extremely slow rate.

Comparing the rates:

• Tertiary alcohols dehydrate fastest due to stable carbocation formation.
• Secondary alcohols are next, slower than tertiary but faster than primary.
• Primary alcohols (with β-hydrogens, e.g., ethanol) dehydrate slowly via E2.
• Methanol cannot dehydrate to an alkene, so it is the slowest.

Thus, the order of dehydration rate is: tertiary > secondary > primary > methanol, or $$3° > 2° > 1° > CH_3OH$$.

Evaluating the options:

• Option A: $$2° > 1° > CH_3OH > 3°$$ → Incorrect, as tertiary is fastest.
• Option B: $$3° > 2° > 1° > CH_3OH$$ → Correct, matches the order.
• Option C: $$2° > 3° > 1° > CH_3OH$$ → Incorrect, as tertiary is faster than secondary.
• Option D: $$CH_3OH > 1° > 2° > 3°$$ → Incorrect, as methanol is slowest.