Effect of the intramolecular hydrogen bond on the electronic structure of organic molecules with a planar quasicycle

The electronic structure of the following organic molecules is studied using the HF/6-311G(d,p) method: malonic dialdehyde, acetylacetone, thiomalonic aldehyde, 2-XC₆H₄NH₂ aniline derivatives, 2-XC₆H₄OH phenol derivatives, 2-XC₆H₄SH thiophenol derivatives (X = CHO, COOH, COO^?, NO, NO₂, OH, OCH₃, SH, SCH₃, F, Cl, Br), 8-hydroxyquinoline, 8-mercaptoquinoline, tropolone. It is found that the intramolecular hydrogen bond (IHB) leads to a local electronic redistribution in the quasi-cycle, and above all to the electron density transfer among the immediate participants of IHB — from the hydrogen atom to the proton-acceptor atom. When the IHB of the S-H?O type forms, the electron density mainly decreases on sulfhydryl hydrogen atom and increases on sulfur atom.