Consider the following bonds:
(I) the C–C bond in ethane,
(II) the C–N bond connecting the carbonyl carbon and nitrogen in acetamide,
(III) the C=C bond in ethene.
Which sequence lists these bonds in order of increasing barrier to rotation about the bond axis?
a) II<I<III
b) I<III<II
c) I<II<III
d) III<II<I