Question #0c15a

1 Answer
Apr 30, 2017

Here is my explanation.


Resonance is the ability of a molecule (or ion or free radical) to be represented by more than one reasonable Lewis structure that differ only in the location of the π electrons

An example is the acetate ion, which has two equivalent resonance structures.

In the English language, mesomerism is an old term for resonance.

The mesomeric effect is the electron-donating or electron-withdrawing effect of a group because of resonance.

For example, carbon 3 in propenal has a slight positive charge because the aldehyde group withdraws electrons through resonance.

The aldehyde group has a –M effect.

-M effect
(From Difference Between)

Similarly, carbon 4 in 1 methoxy-1-3 butadiene has a partial negative charge because the methoxy group donates electrons through resonance.

The methoxy group has a +M effect.