Appearance energies for molecular and some fragment ions from 3-methyl-3-acetyl-, 1,2-dimethyl-3-acetyl-, 1,2-dimethyl-3hydroxycarbonyl-and 1,3-dimethyl-2-(1-methyl)vinylcyclopropenes and model compounds 2,3-dimethylfuran and 1-methylindene were measured by photoionization mass spectrometry. It was shown that, in all cases, the structure of the [M-Me] + ion does not correspond to the expected structures of substituted cyclopropenium ions. Possible schemes for formation of [M-Me] + ions are given. Isodesmic reactions were systematically applied for calculation of the heats of formation for 35 possible C 5 H 5 O + isomers from 3methyl-3-acetyl-cyclopropene. In addition, the heats of formation for more than 30 other unsaturated ions and free radicals were estimated with the help of series of isodesmic reactions. A new value of 160 kJ mol-1 , as compared with the currently used value of 215.5 kJ mol-1 , for the cyclopropylmethyl free radical is suggested. The publication represents the further development of the methodology for the heat of formation estimation procedure for even-electron ions and free radicals.
An empirical method is proposed by which the heats of combustion of oxygenated hydrocarbon oils, typically found from wood pyrolysis, may be calculated additively from empirically predicted heats of combustion of individual compounds. The predicted values are in turn based on four types of energetically inequivalent carbon and four types of energetically inequivalent hydrogen atomic energy values. A method is also given to estimate the condensation heats of oil mixtures based on the presence of four types of intermolecular forces. Agreement between predicted and experimental values of combustion heats for a typical mixture of known compounds was ± 2% and < 1% for a freshly prepared mixture of known compounds.
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