IIT-JEE 2009 · Paper 2 · Chemistry Q4 · Dronacharya Exams

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ChemistrySingle correct+3 / -1Question 4 of 57

The correct stability order of the following resonance structures is

Four resonance structures of diazomethane: (I) H₂C=N⁺=N⁻; (II) H₂C⁺-N=N⁻; (III) H₂C⁻-N⁺≡N; (IV) H₂C⁻-N=N⁺.

A

(I) > (II) > (IV) > (III)

B

(I) > (III) > (II) > (IV)

C

(II) > (I) > (III) > (IV)

D

(III) > (I) > (IV) > (II)

Answer and worked solution

Official answer: B

Criteria: complete octets first, then the negative charge on the more electronegative atom.

(I) H₂C=N⁺=N⁻: every atom has an octet; negative charge on N.
(III) H₂C⁻-N⁺≡N: every atom has an octet, but the negative charge is on carbon.
(II) H₂C⁺-N=N⁻: carbon has only a sextet.
(IV) H₂C⁻-N=N⁺: the terminal nitrogen has a sextet with a positive charge, worst of all.

Order: I > III > II > IV.

(B)

Topics:Resonance Electronic effects (inductive, resonance, hyperconjugation)

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