Question

The correct stability order of the following resonance structure is:
I) $H_{2}C=\stackrel{+}{N}=\stackrel{-}{N}$ II) $H_2\stackrel{+}{C}-N=\stackrel{-}{N}$ III) $H_{2}C-\stackrel{+}{N}=N$ IV) $H_2\stackrel{-}{C}-N=\stackrel{+}{N}$

• A. I > II > IV > III
• B. I > III > II > IV
• C. II > I > III > IV
• D. IiI > I > IV > II

Answer 1

Answer: (B)

I > III > II > IV

(i) Number of $\Pi$ bonds $\alpha$ Resonance energy $\alpha$ stability

(ii) Contributing structures should be such that negative charge resides on an electronegative element and positive charge resides on electro-positive element.

(iii) In contributing structures, like charges should not reside on atoms close to each other and unlike charges should be widely separated.

So, $I>III>II>IV$ is the correct stability order of resonance structures given.

$({CH}_2=N^{+}=N^{-})>(H_{2}C-N^{+}=N)>({CH}_2^{+}-N=N^{-})>({CH}_2^{-}-N=N^{+})$