Concept:

Reactions involving the cleavage of the O-H bond in alcohols rely on the alcohol acting as an acid (donating a proton) or as a nucleophile. The reactivity is governed by the stability of the resulting alkoxide ion or the steric hindrance of the nucleophilic oxygen.

Formula:

$$ \text{R-O-H} \longrightarrow \text{R-O}^- + \text{H}^+ $$

Solution:

• Alkyl groups are electron-donating (+I effect).



• Tertiary alcohols have three alkyl groups, severely destabilizing the negatively charged alkoxide ion due to intense electron repulsion, making the O-H bond harder to break heterolytically.



• Primary alcohols have only one alkyl group, making their alkoxide ion relatively more stable (and the oxygen less sterically hindered).



• Therefore, the reactivity order for O-H bond cleavage is Primary > Secondary > Tertiary.

Why other options are incorrect:

Option C is the correct reactivity order for reactions where the C-O bond breaks (which depends on carbocation stability, where 3° > 2° > 1°). The question specifically asks about O-H bond cleavage.