Answer to Question #166405 in Organic Chemistry for Hafiz Faizal

Question

3.(b) (i) Explain why o-nitrophenol has lower boiling points and lower water solubility as compared

with their m- and p- isomers.

(ii) Compare the acidity of ethanol and phenol by using dilute sodium hydroxide aqueous

solution. Explain why such acidity is observed

Answer 1

(i) Due to intramolecular H-bonding, −OH group is not available to form a hydrogen bond with water. Hence o-nitrophenol is sparingly soluble in water and has lower boiling point while m- and p-nitrophenol are soluble due to intermolecular H-bonding with water and hence they have more boiling point as compared with o-nitrophenol.

(ii) Two reactions that show the acidic nature of phenol are as follows: (a) The reaction of phenol with sodium to form sodium phenoxide with liberation of hydrogen gas. $C_6H_5OH+Na\rightarrow C_6H_5-ONa+\dfrac{1}{2}H_2\uparrow$

(b) The reaction of phenol with sodium hydroxide to give sodium phenoxide and water.

$C_6H_5-OH+NaOH\rightarrow (C_6H_5-O^-)Na^+ +H_2O$

Deprotonation of phenol gives phenoxide ion which is resonance stabilized.

There is no resonance stabilization for the deprotonation of ethoxide ion (obtained by deprotonation of ethanol).

Hence, phenol is more acidic than ethanol.