Question

The enolic form of butanone contains
A. `12 sigma` bonds, `1pi` bond, and 2 lone pairs of electrons
B. `11sigma` bonds, `1pi` bond, and 2 lone pairs of electrons
C. `12sigma` bonds, `1pi`, and 1 lone pair of electrons
D. `10sigma` bonds, `2pi` bond, and 2 lone pairs of electrons

Answer 1

Correct Answer - A
Butanone exhibits tautomerism:

The complete structural formula of enol form is
`H-overset(H)overset(|)underset(H)underset(|)C-overset(H)overset(|)underset(H)underset(|)C-overset( :overset( .. )O-H)overset(|)C=underset(H)underset(|)C-H`
Every single bond is a `sigma` bond, and a double bond consists of one `sigma` bond and one `pi` bond. Thus, it has `12 sigma` bonds, `1pi` bond, and `2` lone pairs of electrons. Note that the same result is obtained from the keto form also.