Valence topological charge-transfer indices for dipole moments
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Valence topological charge-transfer (CT) indices are applied to the calculation of dipole moments. The dipole moments calculated by algebraic and vector semisums of the CT indices are defined. The combination of the CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moment of the valence-isoelectronic series of benzene and styrene. Two CT indices, μvec (vector semisum of vertex-pair dipole moments) and μ V vec (valence μvec) are proposed. μvec and μ V vec are important for the prediction of μexperiment, because (μexperiment−μvec) and (μ V vec−μexperiment) always have the same sign. In general, the best results are obtained for the greatest group that can be studied. The inclusion of the heteroatom in the π-electron system is beneficial for the description of the dipole moment, owing to either the role of additional p and/or d orbitals provided by the heteroatom or the role of steric factors in the π-electron conjugation. The steric effect is almost constant along the studied series and the dominating effect is the electronic one. Inclusion of the heteroatom enhances the dipole moment, which, in turn, can improve the solubility of the molecule. Inclusion of the heteroatom enhances the dipole moment, which can improve the solubility of the molecule.
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