M-2384 J. Chem. Thermodynamics 1989, 21. 859-865 Structural effects on the thermochemical properties of carbonyl compounds I. Enthalpies of combustion, vapour pressures and enthallpies of sublimation, and enthalpies of formation of 2-methylpropanamide, 2,2-dimethylpropanamide, und 1 -adamantyl carboxamide J.-L. M. ABBOUD. P. JIMfiNEZ, M. V. ROUX, C. TURRIdN, Institute of Physical Chemistry “Rocasolano”, C.S.I.C., Serrano 119, 28006 Madrid, Spain and C. LbPEZ-MARDOMINGO Department of Organic Chemistry, University of Alcali de Henares, Campus Universitario, E-28871 Alcaki de Henares (Madrid), Spain (Received 14 April 1989; in jinal form 12 May 1989) The energies of combustion of 2-methylpropanamide, 2,2-dimethylpropanamide, and I-adamantyl carboxamide have been determined using a static bomb calorimeter. The vapour pressureshave been measured over a temperature range of about 15 K by the Knudsen-effusion technique. From the experimental results the following quantities for the three compounds, at 298.15K, have been derived: Compound Wi&) kJ.mol-’ 2-Methylpropanamide -368.6kO.9 86.OkO.2 2,2-Dimethylpropanamide -399.151.3 86.6kO.4 I-Adamantyl carboxamide -427.0k2.4 108.0+0.5 The structural effects on the thermochemical properties have been studied. -282.6kO.9 -313.1 &-1.4 -319.Ok2.5 1. Introduction The gas-phase proton affinities “PA”s”’ (i.e. the standard enthalpy changes for reaction 1 in the gas phase) of carbonyl compounds, XCOY, span a range of some 0021~9614/89/080859+07 %02.00/O 0 1989 Academic Press Limited