The electron density distribution over the C 1 -H 1 -OMeO region in the TS1-3x graphs can be visualized as different patterns. As it was noted above, for the TS1 1-3 b, C 1 -N 1 bcp was localized in a charge depletion zone while H 1 -OMeO bcp was placed in a charge concentration region. Thus, in the C 1 -H 1 -OMeO region there is a clear discontinuity of the charge concentration zone interrupted by a charge depletion zone between C 1 and H 1 . In TS11-3h graphs a continuous zone of charge concentration over C 1 -H 1 -OMeO was observed, indicating a great strength of these interactions. In the TS11-3d graphs, the C 1 -H 1 bcp was in a charge concentration zone and had a charge distribution pattern that was between those of TS1-3b and TS1-3h. This pattern is consistent with experimental results, as the 4-Cl-C6H4 group was found to be the inflection point of both mechanisms. In addition, there are greater changes in the charge density distribution due to the substituents effect in TS1-3x than in TS1-2x, which is in line with the larger dependence on the aryl substituent found for the prototropic mechanism. The peculiarities in the electron density distribution could be useful to identify substrates that may follow the prototropic mechanism.