J. R. Gomes, Emanuel A. Sousa, J. Gonçalves
Jul 1, 2007
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0
Influential Citations
9
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Journal
Journal of Physical Organic Chemistry
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 NO 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 NO bonds for quinoxaline 1,4-dioxide derivatives. As found previously, similar NO bond lengths in quinoxaline-1,4-dioxide compounds are not linked with NO bonds having the same strength. Copyright © 2007 John Wiley & Sons, Ltd.