Imidazole-tetramethylammonium complex

The interactions between tetramethylammonium (TMA) and tt systems may be described as strong CH/tt interactions, as these systems have short contacts between the C - H bonds and the tt system. However, the physical origin of the attraction in the TMA complex is completely different from that in the CH/tt interaction between neutral molecules [124,125). The MP2-level interaction energies of TMA complexes with benzene, pyrrole, furan and imidazole are -8.45, - 10.02, -6.98 and - 16.37 kcal/mol, respectively. The calculations show that the electrostatic interaction is the major somce of the attraction in these complexes, while dispersion is mainly responsible for the attraction in the CH/tt interaction between neutral molecules. The physical origin of the attraction between the TMA and tt systems is the same as that of other cation/Tr complexes therefore, the interaction between TMA and tt systems is essentially a cation/Tr interaction (see the next section). 

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