Hydrogen bonding plays a central role in the following phenomena [IIT-ADVANCED-2014
- Ice floats in water
- Higher Lewis basicity of primary amines than tertiary amines in aqueous solutions
- Formic acid is more acidic than acetic acid
- Dimerization of acetic acid in benzene.
lce has cage-like structure in which each water molecule is surrounded by four other water molecules
tetrahedrally through hydrogen boding, due to this density of ice is less than water and it floats in water
The conjugate acid of methylamine and trimethylamine will be stabilized by three and one H-bonding respectively. Hence, conjugate acid of primary amine is more stable than the conjugate acid of tertiary amine. Hence, the higher Lewis basicity of primary amines than tertiary amines in aqueous solutions is solely due to H-bonding
Formic acid is more acidic than acetic acid due to the electron donating +I effect of methyl group present in acetic acid which make the conjugate base of acetic acid unstable.
Acetic acid remain as dimer in benzene through the formation of intermolecular H-bonding
dimerization of acetic acid by intermolecular H-bond
Hence, the correct answer is : (1, 2, 4).