Question

Identify a more favourable resonance structure from the following. Justify.

\[\begin{array}{cc}
\phantom{.............}\ce{O-}\phantom{......................}\ce{O+}\\\phantom{............}|\phantom{.........................}|\\
\ce{^{+}CH3 - CH = C - H ↔ ^{-}CH2 - CH = C - H}
\end{array}\]

Answer 1

\[\begin{array}{cc}
\phantom{.............}\ce{O-}\phantom{......................}\ce{O+}\\\phantom{............}|\phantom{.........................}|\\
\ce{^{+}CH3 - CH = C - H ↔ ^{-}CH2 - CH = C - H}
\end{array}\]

                    (I)                                     (II)

Both structures (I) and (II) involves the separation of opposite charges, but structure (I) has a positive charge on the more electropositive ‘C’ and a negative charge on more electronegative ‘O’. Thus, structure (I) will be a more favourable resonance structure.