A computational study on the energetics and reactivity of some xanthene and thioxanthene derivatives
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ORIGINAL RESEARCH
A computational study on the energetics and reactivity of some xanthene and thioxanthene derivatives Vera L. S. Freitas • Jose´ R. B. Gomes Maria D. M. C. Ribeiro da Silva
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Received: 23 July 2012 / Accepted: 23 August 2012 / Published online: 8 September 2012 Ó Springer Science+Business Media, LLC 2012
Abstract A computational study has been carried out for xanthene and thioxanthene homologous derivatives with keto, hydroxyl, carboxyl, and carboxamide functional groups on position 9, contributing to the understanding of their energetics and reactivity. For that it is presented and compared with the molecular structures, the electrostatic potential energy maps, and the electronic properties of all these heteropolycyclic compounds. The estimation of the standard molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, was made only for the thioxanthydrol, thioxanthene-9-carboxylic acid, and thioxanthene-9-carboxamide using the experimental values available in the literature for the homologous compounds containing oxygen. Keywords Electrostatic potential energy map Electronic properties HOMO LUMO Enthalpy of formation
Introduction Heteropolycyclic compounds have revealed to be substances with peculiar chemical and/or biochemical characteristics, Electronic supplementary material The online version of this article (doi:10.1007/s11224-012-0117-9) contains supplementary material, which is available to authorized users. V. L. S. Freitas M. D. M. C. Ribeiro da Silva (&) Centro de Investigac¸a˜o em Quı´mica, Departamento de Quı´mica e Bioquı´mica, Faculdade de Cieˆncias, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal e-mail: [email protected] J. R. B. Gomes CICECO, Departamento de Quı´mica, Universidade de Aveiro, Campus Universita´rio de Santiago, 3810-193 Aveiro, Portugal
lending them important properties with wide applications in several areas. For these reasons, such compounds are the target of many studies, in attempt to understand the intrinsic features responsible for such properties and aiming for their improvement. The peculiarities of this class of compounds attracted our attention and determined our involvement in an experimental and/or computational systematic thermochemistry study of polycyclic compounds composed by two benzenic rings fused to a heteroatomic central ring, pentagonal or hexagonal, containing oxygen or sulfur, such as dibenzothiophene [1] and their methyl derivatives [2, 3], or xanthene [4] and their correspondent keto (9-xanthone) [5], hydroxyl (9-xanthydrol) [6], carboxyl (xanthene-9-carboxylic acid) [6] and carboxamide (xanthene-9-carboxamide) [6] derivatives, or thioxanthene [7] and its keto derivative (9-thioxanthone) [8] among others that are currently being studied. Some of the molecules studied are the substructures of organic compounds with marked and effective physiological activities, being important for the synthesis of new pharmacological active compounds. In fact, xanthene derivatives can exhibit specific biologica
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