Chemistry · Amines · NEET
Amines DO form hydrogen bonds. The N-H bond has a partial positive H that bonds to the lone pair on N of another molecule. But because N is less electronegative than O, these N-H hydrogen bonds are weaker than the O-H hydrogen bonds in alcohols. So amines boil lower than alcohols of similar mass, but still boil higher than alkanes (which have no hydrogen bonding at all).
Electronegativity is how strongly an atom pulls bonding electrons. O pulls harder than N, so in O-H the H becomes more positive and the O becomes more negative. This stronger charge separation makes the hydrogen bond between molecules stronger. In N-H the pull is smaller, the charges are smaller, so the hydrogen bond is weaker and easier to break.
Ethanol (C2H5OH, ~46 u) boils at about 351 K; ethylamine (C2H5NH2, ~45 u) boils at about 289 K. The mass is nearly the same, so mass is not the reason. The only big difference is O-H hydrogen bonding in ethanol versus weaker N-H hydrogen bonding in ethylamine. Stronger hydrogen bonds in ethanol need more heat to break, giving the higher boiling point.
Strength of a hydrogen bond depends on the electronegativity difference. O-H has a bigger electronegativity gap than N-H, so O-H forms a stronger, more polar bond and a stronger intermolecular hydrogen bond. Same idea explains why HF (F very electronegative) hydrogen bonds strongly. The trend for boiling points is: acids/alcohols (O-H) > amines (N-H) > alkanes (no H-bond).
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Ethanol boils higher (about 351 K vs about 289 K) because O-H hydrogen bonding is stronger than N-H hydrogen bonding, even though their molecular masses are almost equal.
Yes. Amines have N-H hydrogen bonding, alkanes have none. So the order is alcohol > amine > alkane for comparable molecular mass.
Yes. Tertiary amines have no N-H bond, so they cannot form intermolecular hydrogen bonds. The order is primary > secondary > tertiary amine. This is a separate NEET point covered in the next concept.
No. Ethylamine and ethanol have almost identical masses. The difference comes only from the strength of hydrogen bonding, which depends on electronegativity (O vs N).
