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+.