CHEMISTRY TEXTBOOK

Problem 11.3 : The boiling points of n-butyl
alcohol, isobutyl alcohol, sec-butyl alcohol
and tert-butyl alcohol are 118^0 C, 108^0 C.
99.5^0 C and 83^0 C respectively. Explain.

Solution : As branching increases
intermolecular van der Waal’s force become
weaker and the boiling point decreases.
Therefore n-butyl alcohol has highest
boiling point 118^0 C and tert-butyl alcohol
has lowest boiling point 83^0 C. Isobutyl
alcohol is a primary alcohol and hence its
boiling points is higher than that of sec-
butyl alcohol.

d. Solubility : Phenols and lower alcohols

(having upto three carbons) show appreciable

solubility in water due to their ability to form

intermolecular hydrogen bonding with water

molecule (See Table 11.5).

Table 11.5 M.P/B.P and solubilities of some alcohols and phenols

Name Formula M.P. (^0 C) B.P. (^0 C) Solubility (g/100g H 2 O)

Methyl alcohol H 3 C-OH -97 65 0.793

Ethyl alcohol H 3 C-CH 2 -OH -115 78 0.789

n-Propyl alcohol H 3 C-CH 2 -CH 2 -OH -126 97 0.804

Isopropyl alcohol H 3 C-CH-OH

CH 3

-86 83 0.789

n-Butyl alcohol H 3 C-CH 2 -CH 2 -CH 2 -OH -90 118 0.810

Isobutyl alcohol H 3 C-CH-CH 2 -OH

CH 3

-108 108 0.802

sec-Butyl alcohol H 3 C-CH 2 -CH-OH

CH 3

-114 99.5 0.806

tert-Butyl alcohol

H 3 C C-OH

H 3 C

H 3 C 25.5^83 0.789

Phenol

OH

41 182 9.3

p-Cresol

H 3 C OH

35 202 2.3

o-Nitrophenol

NO 2

OH^45217 0.2

p-Nitrophenol

O 2 N OH

114 - 1.7

R-O Ar-O

H H H H

H H

H H

O O

H O H O

Intermolecular hydrogen bonding

of R-OH and Ar-OH with water

δ⊕ δ⊕

δ⊕ δ⊕

δ-

δ-

δ-

δ-

Hydrogen

Hydrogen bond

bond