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Theoretical quantities pertaining to the two methods of approximation used in the molecular orbital treatment of problems of chemical reactivity of conjugated systems are compared. For alternant hydrocarbons which are not radicals, the correlations which can be established between pairs of these theoretical quantities are ambiguous. In the treatment of mono derivatives, however, unique correlations may be obtained on the basis of a corresponding dependency upon the energy parameter representing the hetero system. A similar characteristic dependency is shown experimentally in some of the different types of reactions involving these systems.

Ab initio MO computations have been carried out for the crystalline form of the B, vitamin, pyridoxinium chloride. In the crystal, the pyridoxine is protonized to pyridoxinium, with the formation of a hydrogen bond N-H+ . * * CI-. For an isolated molecule, the calculations predict a single potential well, with H+ placed close to CI-at the minimum. When neighboring molecules are included in the calculations, a double well is formed, and the lower minimum occurs for the proton placed near the experimentally observed position, in the vicinity of the N atom.Mulliken populations, which depend on the proton position, are described.

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The free valence of a carbon atom in a conjugated hydrocarbon calculated by using &ax = 3 + 4 3 is characteristic of the available bonding power of the atom and independent of the system ultimately bonded, and is ideally linearly related to the energy required to localize one T electron at the atom.