The Boiling Point Of Comparable Molar Mass

The boiling point of comparable molar mass: Compounds CH3CH2CH2CH3 CH3CH2Cl CH3COCH3 CH3CH2CH2NH2 CH3CH2CH2OH CH3COOH

Relative molar mass 58 64.5 58 59 60 60

Carboxylic acid > alcohol > amine > carbonyl compound ≈ haloalkane > alkane Increasing the boiling point Reason: (i) Alkanes are non-polar molecules (van der waals forces) & cannot form hydrogen bond (ii) Haloalkanes and carbonyl compounds cannot form hydrogen bond although they are polar compounds (van der waals forces)

Dipole-dipole interactions tarikan dwikutub-dwikutub (van der Waals forces) (daya van der waals)

δ- O

C δ+

δ+ C

O δ-

Dipole-dipole interactions tarikan dwikutub-dwikutub (van der Waals forces) (daya van der waals)

(iii) Amine, alcohol and carboxylic acid can form inter-molecular hydrogen bonds (iv) The hydrogen formed between amine molecules is weaker than alcohol since nitrogen atom less electronegative than oxygen (v) The boiling point of carboxylic acid is higher than alcohol because the molecules exist as stable dimers through hydrogen bonding. The molecules are closer and the hydrogen bonds are stronger in comparison with alcohol hydrogen bond

H

O R

O

C

C O

H

O

hydrogen bond

R