Question

The decreasing order of boiling points of the following alcohols is?

• A. $\text{3-methylbutan-2-ol > 2-methylbutan-2-ol > pentan-1-ol}$
• B. $\text{pentan-1-ol > 3-methylbutan-2-ol > 2-methylbutan-2-ol}$
• C. $\text{2-methylbutan-2-ol > 3-methylbutan-2-ol > pentan-1-ol}$
• D. $\text{2-methylbutan-2-ol > pentan-1-ol > 3-methylbutan-2-ol}$

Answer 1

The correct option is B $\text{pentan-1-ol > 3-methylbutan-2-ol > 2-methylbutan-2-ol}$

$\text{3-methylbutan-2-ol}\left(C{H}_{3}CH\right(C{H}_3\left)CH\right(OH\left)C{H}_3\right)$ is a secondary alcohol.
$\text{2-methylbutan-2-ol}\left(C{H}_{3}C{H}_{2}C\right(C{H}_3\left)\right(OH\left)C{H}_3\right)$ is a tertiary alcohol.
$\text{pentan-1-ol}\left(C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}C{H}_{2}OH\right)$ is a primary alcohol.

For same molecular formula, as branching in chain of alcohol increases​ surface area decreases​ due to which van der Waals force decreases​ and thus Boiling point decreases​. Therefore the decreasing order of boiling point is primary alcohol > secondary alcohol > tertiary alcohol. So order of boiling point is
$\text{pentan-1-ol > 3-methylbutan-2-ol > 2-methylbutan-2-ol}$.