Heats of formation and protonation thermochemistry of gaseous benzaldehyde, tropone and quinone methides

Quantum chemistry calculations using composite G3B3, G3MP2B3 and CBS-QB3 methods were performed for benzaldehyde, 1, tropone, 2, ortho-quinone methide, 3, para-quinone methide, 4, their protonated forms 1H(+)-4H(+) and the isomeric meta-hydroxybenzyl cation 5H(+). The G3B3 298 K heats of formation values obtained in this work are: -39, 61, 52, 39, 661, 679, 699, 680 and 733 kJ mol(-1) for 1-4, 1H(+)-5H(+), respectively. At the same level of theory, computed proton affinities are equal to 834, 916, 887 and 892 kJ mol(-1) for molecules 1-4. These results allow to correct discrepancies on the previously reported thermochemistry of molecules 2-4 and cations 2H(+)-5H(+). (C) 2010 Elsevier B.V. All rights reserved.