Explain why many amines with useful medicinal properties are sold as their ammonium salts

Compare N-methylacetamide with its amide isomers propanamide and N,N-dimethylformamide. Which do you predict has the highest boiling point? The lowest?

N-Methylpyrrolidine has a boiling point of 81 °C, and piperidine has a boiling point of 106 °C. Tetrahydropyran has a boiling point of 88 °C, and cyclopentanone has a boiling point of 141 °C. These two isomershave a boiling point difference of 53 °C. Explain why the two oxygen-containing isomers have a much larger boilingpoint difference than the two amine isomers