"No charge separation" meaning? [ENDORSED]

[Davis Chong 4H]

Hey y'all,

On pg 166 on the Intro to Organic Chemistry book, it says "The bonding in ethanamide is very similar to nitroethane, but its two resonance contributors are not equal in energy. The resonance structure on the left is more stable as there is no charge separation.

What exactly does this mean?

[Lauren_Johnston_3F]

I believe it is the space between particles of opposite charges, but I am not entirely sure.

[Rachel Kipp 1I]

Recall from Chem 14A the concepts of Resonance and Formal Charge. The better resonance structure would have the lower formal charge. Formal charge is calculated by (# of Valence Electrons) - (# of non-bonding electrons + ((1/2)(bonding electrons)).

So the no charge separation refers to the resonance structure on the left being more stable due to its O atom having 0 formal charge, versus the structure on the right with a -1 formal charge on the O atom.

[Laura_funes_1j]

Resonance structures are used instead of single Lewis structures to better show the delocalized electrons in a molecule. For resonance structures, we want to minimize the charge so we want to minimize charge separation. Charge separation is basically the amount of positive and negative charges in a structure, so we always want to try to have the one with the least amount of charge and the one with more spread out charge. This causes stability in resonance structures. So having no charge separation means that it is the best resonance structure to use because it has minimized charge.