Question

In which of the following, resonance is not possible?

• A. 1, 2
• B. 2, 4
• C. 3, 4
• D. 1, 4

Answer 1

The correct option is B

2, 4

The explanation for the correct option:

Condition for resonance:

1. The Pi-bond is present at an alternate position to the atom bearing a vacant orbital.

eg. $H_{2}C=CH-X^{+}$

2. The Pi-bond is present at the alternate position to the atom bearing a negative charge.

eg. $H_{2}C=CH-X^{-}$

3. A Pi-bond is present at the alternate position to the atom bearing a lone pair of electrons.

eg. $H_{2}C=CH-X_{*}^{*}$

4. Pi- bond present at the alternate position to the atom bearing lone electron.

eg. $H_{2}C=CH-\stackrel{*}{X}$

5. A Pi-bond is present at the alternate position to another Pi-bond.

eg. $H_{2}C=CH-CH=C{H}_2$

Molecules (1) and (3) are obeying the above conditions.

The explanation for the incorrect option:

Molecules (2) and (4) are not obeying any of these conditions mentioned above.

Hence, (b) is the correct answer.