resumo
In order to understand the influence of the methyl group in the stability of the indole unit, the standard (p degrees = 0.1 MPa) molar enthalpies of formation of 1-, 2-, and 3-methylindoles, in the gaseous phase, were determined at T = 298.15 K. For that, combustion calorimetry was used to determine the massic energies of combustion and consequently the standard molar enthalpies of formation in the condensed phase, and Calvet microcalorimetry was employed to measure the standard molar enthalpy of phase transition (vaporization for the liquid 1-methylindole and sublimation for the other two solid compounds). The G3(MP2)//B3LYP composite approach was used to calculate the gas-phase enthalpies of formation, at T = 298.15 K, of all possible single methylated indoles using four different working reactions. The enthalpies calculated for the 1-, 2-, and 3-methylindoles are in excellent agreement with the values derived from the experimental work. (C) 2009 Elsevier Ltd. All rights reserved.
palavras-chave
3-METHYLINDOLE; INDOLE; CALORIMETRY; ENTHALPIES; COMBUSTION
categoria
Thermodynamics; Chemistry
autores
da Silva, MAVR; Cabral, JITA; Gomes, JRB
nossos autores
José R. B. Gomes
Investigador Principalagradecimentos
Thanks are due to Fundacao para a Ciencia e Tecnologia (FCT), Lisbon, Portugal and to FEDER for financial support. J.I.T.A.C. thanks FCT and the European Social Fund (ESF) under Community Support Framework (CSF) for the award of a Post-Doc research grant (BPD/27140/2006).