"Weights Watcher" for mesomeric structures: A straightforward approach to get the weight of a mesomeric structure is discussed. Weights of Lewis structures can be computed using various ab initio approaches, but this require some knowledge in using quantum chemistry packages.

We present here a straightforward alternative, based on the Interaction between Lewis Configurations and using Hückel energies. The approach is thus based of the Hückel Hamiltonian and embeds simple Lewis concepts. Our scheme has been named "Hückel-Lewis CI" (HL-CI) because of these underlying specificities.

It gives an immediate access to the weights involved in mesomery. Drawbacks of this approach are identified and the accuracy is discussed on typical systems including acrolein, uracil, pyrrole-like systems and imidazolylidene.

The HL-CI scheme, published in J. Chem. Educ. for the 2x2 mesomeric case, is thus extended here to any NxN mesomery.

Note that we obtain the weights from the resonance energies.