Question

Which of the following alcohols will give the most stable carbocation during dehydration?

• A. 2-Methyl -1- propanol
• B. 2-Methyl -2- propanol
• C. 1-Butanol
• D. 2-Butanol

Answer 1

The correct option is B 2-Methyl -2- propanol

Alcohol $+H_{2}S{O}_4\to$ Alkene

The dehydration reaction is an elimination reaction that goes via carbocation formation as shown in the figure.

Tertiary carbocations are most stable due to + Inductive effect of alkyl groups, then is secondary and least stable is primary. Therefore the reactivity and stability of carbocation follow the order as

Tertiary alcohol>secondary alcohol>primary alcohol

2-Methyl-1-propanol forms secondary carbocation as: $(C{H}_3{)}_{2}CHC{H}_2^{+}$

2-Methyl-2-propanol forms tertiary carbocation as: $(C{H}_3{)}_3{C}^{+}$

1-Butanol forms primary carbocation as: $C{H}_{3}C{H}_{2}C{H}_{2}C{H}_2^{+}$

and 2-Butanol forms secondary carbocation as: $C{H}_{3}C{H}^{+}C{H}_{2}C{H}_3$

Thus most stable carbocation is formed by 2-Methyl -2- propanol during its dehydration.