Question

(I) 1,-dihydroxy benzene (II) 1,3-dihydroxyl benzene (III) 1,4-dihydroxy benzene (IV) Hydroxyl benzene
The increasing order of boiling point of above mentioned alcohols is
A. ` I lt II lt III lt IV`
B. `I lt II lt IV lt III`
C. `IV lt I lt II lt III`
D. `IV lt II lt I lt III`

Answer 1

Correct Answer - C
1,4-dihydroxy benzene shows the highest boiling point among given compounds because it form strong intermolecular hydrogen bond (It does not form intramolecular H-bonding) .

Order of H-bonding in o, m and p-isomers of a compound is given below.
intermolecular H-bonding `o lt m lt p` -isomers
Intramolecular H-bonding `o gt m gt p`-isomers
Hydroxy benzene do not form a chain of H-bonding Hence, intermolecular H-bond is stronger then intramolecular H-bond , so the stability of 1,4-dihyroxy benzene is highest . Hence, its boiling point is highest . The increasing order of the boiling points of the given compounds is
`IV lt I lt II lt III`