Question

Give reason for the following:

The melting points of alkanes with odd no. of carbon atoms are lower than those with even numbers of carbon atoms.

Answer 1

n-alkanes with even no. of carbon atoms have methyl groups in opposite directions and fit better in the crystal lattice than n-alkanes with odd number of carbon atoms have methyl groups in same directions and do not fit better in the crystal lattice and hence pack loosely in the crystal lattice.