Chemistry - GOC Question with Solution | TestHub

Resonating structures differ only in the position of electrons (π bonds and lone pairs). The atoms and the sigma skeleton must stay in the same place.

(A) $\mathrm{C}{\mathrm{H}}_3\mathrm{CHO}$ and $\mathrm{C}{\mathrm{H}}_2=\mathrm{CH}-\mathrm{OH}$ differ in the position of a hydrogen atom: they are keto-enol tautomers, not resonating structures.

(B) $\mathrm{C}{\mathrm{H}}_2=\mathrm{CH}-{\mathrm{O}}^{-}$ and ${}^{-}\mathrm{C}{\mathrm{H}}_2-\mathrm{CH}=\mathrm{O}$ have the same atoms in the same places. Only the π electrons and the negative charge move (enolate ion). Valid.

(C) $\mathrm{C}{\mathrm{H}}_3\mathrm{CONHC}{\mathrm{H}}_3$ and $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{CON}{\mathrm{H}}_2$ have different skeletons: constitutional isomers.

(D) Nitroethane and ethyl nitrite are linked through different atoms (N versus O): linkage isomers.

Answer: (B).