Resonance and Delocalization - Organic Chemistry Concepts: An EFL Approach - page 62

C The two most important resonance forms for each are:
The dipolar form in the first example is the minor one, but it is still important. It is a
simple extension of the concept shown earlier in Program 9A. It shows the electron
movement extended into the adjacent conjugated C ] C double bond. This structure
helps explain the effect that the electronegative oxygen has on the carbon center that
is three atoms away.
The second example simply shows the two localized structures that are the major
resonance forms for the aromatic benzene system.
Q 4.3. Use the ideas from Program 11 to draw resonance forms for:
PROGRAM 12 Delocalization
A This topic does not give a full description of the resonance concept in aromatic
systems. The Programs mentioned earlier are the basis to understand delocalization,
especially of charged systems. This helps us understand the relative reactivity and
stability of species.
The concepts explained earlier only show ionic species. This can also be done for
radical species with unpaired electrons by using curly arrows with single heads.
A single-headed arrow shows the movement of single electrons rather than pairs.
For example, resonance delocalization in the allylic radical is shown below.