Energetic and structural characterization of 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl): experimental and computational studies |
| |
| Authors: | José R. B. Gomes Emanuel A. Sousa Jorge M. Gonçalves Luís Gales Ana M. Damas Paula Gomes Siddharth Pandey William E. Acree Jr Maria D. M. C. Ribeiro da Silva |
| |
| Affiliation: | 1. Centro de Investiga??o em Química (CIQ), Departamento de Química, Faculdade de Ciências, Universidade do Porto (UP), Rua do Campo Alegre 687, P‐4169‐007 Porto, Portugal;2. Instituto de Biologia Molecular e Celular (IBMC) and Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, Portugal;3. Department of Chemistry, Indian Institute of Technology Delhi (IIT‐Delhi), Hauz Khas, New Delhi 110016, India;4. Department of Chemistry, University of North Texas (UNT), Denton, TX 76203‐5070, USA;5. Centro de Investiga??o em Química (CIQ), Departamento de Química, Faculdade de Ciências, Universidade do Porto (UP), Rua do Campo Alegre 687, P‐4169‐007 Porto, PortugalCentro de Investiga??o em Química (CIQ), Departamento de Química, Faculdade de Ciências, Universidade do Porto (UP), Rua do Campo Alegre 687, P‐4169‐007 Porto, Portugal.=== |
| |
| Abstract: | The gaseous standard molar enthalpies of formation of two 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐1,4‐dioxide has been obtained by X‐ray crystallography showing that the two N? O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas‐phase after computations performed at the B3LYP/6‐311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N? O bonds for quinoxaline 1,4‐dioxide derivatives. As found previously, similar N? O bond lengths in quinoxaline‐1,4‐dioxide compounds are not linked with N? O bonds having the same strength. Copyright © 2007 John Wiley & Sons, Ltd. |
| |
| Keywords: | thermochemistry bond dissociation energies density functional theory calculations nitrogen?oxygen bonds |
|
|
