Select the single best answer. why is the boiling point of propanamide, ch3ch2conh2, considerably higher than the boiling point of n, n−dimethylformamide, hcon(ch3)2 (213°c vs. 153°c), even though both compounds are isomeric amides?

The reason for higher boiling point of Propanamide as compared to N,N−dimethylformamide although both are isomers of each other is due to the difference in the intermolecular interactions among their molecules. 

As shown below, propanamide contains two hydrogen atoms directly attached to Nitrogen atom. In this case the hydrogen atoms become partially positive and can form Hydrogen Bond Interactions with the Nitrogen atoms of neighbor propanamide molecule.

Due to the involvement of Hydrogen bonding which is strongest among intermolecular interactions increases the boiling point of propanamide which are absent in N,N−dimethylformamide.