Nonbonded resonance stabilization energies

Resonance effect is an energy stabilization due to delocalization of electrons in the bond network of the molecule and can be attributed to a mesomeric effect, i.e. the delocalization of Jt electrons on the jr orbital network, a hyperconjugation effect, i.e. a delocalization of a electrons in a ji orbital aligned with the o bond, and secondary mesomeric effects, such as repulsion of the ir electrons by nonbonded electrons on a substituent or solvent, or by time-dependent effects due to polarizabilities (for the last, the term electromeric effect is sometimes used). 

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