Question

(I) $1,2$-Dihydroxybenzene (II) $1,3$-Dihydroxybenzene (III) $1,4$-Dihydroxybenzene (IV) Hydroxybenzene
The increasing order of boiling points of above-mentioned alcohols is:

• A. $I<II<III<IV$
• B. $I<II<IV<III$
• C. $IV<I<II<III$
• D. $IV<II<I<III$

Answer 1

The correct option is C $IV<I<II<III$

With an increase in the molecular weight, the boiling point increases. With an increase in $OH$ groups, the extent of hydrogen bonding increases, and boiling point increases.

Due to above two reasons, (IV) Hydroxybenzene has a lowest boiling point.

In case of (I) 1,2-dihydroxybenzene, since two $OH$ groups are in the ortho position, there is intramolecular hydrogen bonding.

In (II) 1,3-dihydroxybenzene and (III) 1,4-dihydroxybenzene, intermolecular hydrogen bonding is present which leads to the molecular association. Hence (I) 1,2-dihydroxybenzene has a lower boiling point than (II) 1,3-dihydroxybenzene and (III) 1,4-dihydroxybenzene.
The increasing order of boiling points of above-mentioned alcohols is (IV) Hydroxybenzene < (I) 1,2-dihydroxybenzene < (II) 1,3-dihydroxybenzene < (III) 1,4-dihydroxybenzene.