Page No. 231

8.1. Write the structures of the following compounds

(i) α-Methoxypropionaldehyde

(ii) 3-Hydroxybutanal

(iii) 2-Hydroxycyclopentane carbaldehyde

(iv) 4-Oxopentanal

(v) Di-sec-butyl ketone

(vi) 4-Fluoroacetophenone

Solution

(i) α-Methoxypropionaldehyde

(ii) 3-Hydroxybutanal

(iii) 2-Hydroxycyclopentane carbaldehyde

(iv) 4-Oxopentanal

(v) Di-sec-butyl ketone

(vi) 4-Fluoroacetophenone

Page No. 234

8.2. Write the structures of products of the following reactions:

Solution

(i) Benzene reacts with C₂H₅COCl, to yield propiophenone (Friedel Craft’s acylation).

(ii) (C₆H₅CH₂)₂Cd + 2CH₃COCl →

(iii) Propyne reacts to form Propanone

(iv) p-Nitrotoluene reacts to form p-Nitrobenzaldehyde

Page No. 236

8.3. Arrange the following compounds in increasing order of their boiling points.

CH₃CHO, CH₃CH₂OH, CH₃OCH₃, CH₃CH₂CH₃

Solution

The molecular masses of the given compounds are in the range 44 to 46. CH₃CH₂OH undergoes extensive intermolecular H-bonding, resulting in the association of molecules. Therefore, it has the highest boiling point. CH₃CHO is more polar than CH₃OCH₃ and so CH₃CHO has stronger intermolecular dipole−dipole attraction than CH₃OCH₃⋅CH₃CH₂CH₃ has only weak van der Waals force.

Thus, the arrangement of the given compounds in the increasing order of their boiling points is given by:

CH₃CH₂CH₃ < CH₃OCH₃ < CH₃CHO < CH₃CH₂OH

Page No. 243

8.4. Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions

(i) Ethanal, Propanal, Propanone, Butanone.

(ii) Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone.

Solution

(i) The +I effect of the alkyl group increases in the order:

Ethanal < Propanal < Propanone < Butanone

The electron density at the carbonyl carbon increases with the increase in the +I effect. As a result, the chances of attack by a nucleophile decrease. Hence, the increasing order of the reactivities of the given carbonyl compounds in nucleophilic addition reactions is:

Butanone < Propanone < Propanal < Ethanal

(ii) The +I effect is more in ketone than in aldehyde. Hence, acetophenone is the least reactive in nucleophilic addition reactions. Among aldehydes, the +I effect is the highest in p-tolualdehyde because of the presence of the electron-donating −CH₃ group and the lowest in p-nitrobezaldehyde because of the presence of the electron-withdrawing −NO₂ group.

Hence, the increasing order of the reactivities of the given compounds is:

Acetophenone < p-tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde