Q.14. Question: Why the boiling point ... [FREE SOLUTION]

Chapter 3: Q.14. (page 91)

Question: Why the boiling point of propanamide $C H_{3} C H_{2} C O N H_{2}$ , is considerably higher than the boiling point of N,N-dimethylformamide, $H C O N {(C H_{3})}_{2}$ ( $213^{0} C$ vs. $153^{0} C$ ), even though both compounds are isomeric amides.

Short Answer

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Answer

The boiling point of propanamide is higher because of its ability to form hydrogen bonds. N,N-dimethylformamide is not able to form hydrogen bonds.

Step by step solution

Factors affecting the boiling point

Intermolecular interactions: Stronger intermolecular interactions lead to higher boiling points of compounds.Hydrogen bonding is the strongest among the intermolecular forces, followed by dipole-dipole interactions, and Van derWaals forces.

The compounds which have higher surfaces tend to have higher boiling points. The compounds with high polarizability also have higher boiling points.

The boiling point of propenamide is higher than the boiling point of N,N-dimethylformamide

The structures of propanamide and N,N-dimethylformamide are shown below:

Propanamide

N,N-dimethylformamide

The boiling point of propanamide will be higher as compared to N,N-dimethylformamide.

Propanamide has stronger intermolecular interactions. In addition to the dipole-dipole interactions, propanamide can also form hydrogen bonds. The hydrogen atoms of the $- N H_{2}$ group can form hydrogen bonds with the neighbouring molecules.

On the other hand, hydrogen bonding cannot take place in N, N-dimethylformamide.