Relation between π-Electron Localization/Delocalization and H-Bond Strength in Derivatives of o-Hydroxy-Schiff Bases

• Published in: Journal of organic chemistry 2008-03, Vol.73 (6), p.2138-2145
• Main Authors: Krygowski, Tadeusz M, Zachara-Horeglad, Joanna E, Palusiak, Marcin, Pelloni, Stefano, Lazzeretti, Paolo
• Format: Article
• Language: English
• Subjects: Chemical reactivity; Chemistry; Exact sciences and technology; Organic chemistry; Reactivity and mechanisms
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo7023174

Detailed investigations of electronic effects taking place within the molecular system of o-hydroxy Schiff bases have been performed. The analysis of geometry, local and global aromaticity, selected AIM-based parameters, and finally, π-electron currents induced in the systems under consideration have been performed on the basis of quantum chemical calculations at the B3LYP/6-311+G** level of theory. The relation between localization/delocalization of π-electrons within the whole system has been described. It has been shown that the character of the bond which is common to the phenylic ring and the quasi-ring formed as a result of H-bond formation has a crucial impact on the strength of H-bonding. The strongest H-bonds can be observed for the systems in which the sequence of formally single and double bonds within the H-bridged quasi-ring enable a π-electronic coupling. These observations indicate that π-electron effects play a fundamental role in the stabilization of the hydrogen bridge within o-hydroxy Schiff bases. Analysis of π-ring currents induced by a magnetic field perpendicular to the molecular plane of selected analyzed systems confirms these conclusions.