Question 3.14: Resonance Contributing Structures Which sets are valid pairs...

Resonance Contributing Structures
Which sets are valid pairs of contributing structures?

{\begin{matrix} &&\underset{||}{\text{:O:}} \\ \text{CH}_{3}&-&\text{C}&-&\text{CH}_{3} \end{matrix}}     and     {\begin{matrix} && \; \underset{|}{:\ddot{\text{O}} :}^{-} \\ \text{CH}_{3}&-&\underset{+}{\text{C}} &-&\text{CH}_{3} \end{matrix}}

(a)

{\begin{matrix} &&\underset{||}{\text{:O:}} \\ \text{CH}_{3}&-&\text{C}&-&\text{CH}_{3} \end{matrix}}    and    {\begin{matrix} &&:\underset{|}{\ddot{\text{O}}}&-&\text{H} \\ \text{CH}_{2}&=& \text{C} &-&\text{CH}_{3} \end{matrix}}

(b)

Strategy
The guideline tested in this example is that contributing structures involve only the redistribution of valence electrons. The position of all atoms remains the same.