Thermochemistry of Organic and Heteroorganic Species. Part IV. Photoionization Studies of Isomerization and Fragmentation of Poly-Substituted Cyclopropenes. 3-Methyl-3-Ethynyl- and Tetrachlorocyclopropene

Appearance energies of [M – Me]⁺ ions from p-ethylphenylacetylene, 1-methyl-1-phenylcyclopropane and 3-methyl-3-ethynylcyclopropene and of [M – Cl]⁺ ions from tetrachlorocyclopropene were measured by photoionization mass spectrometry. The heats of formation 1040.5, 864, 1268 and 1041 kJ mol⁻¹ were obtained for ethynyl- and vinyltropylium and ethynyl- and trichlorocyclopropenium ions, respectively. Using these and some literature data and the series of isodesmic reactions, the heats of formation of seven substituted cyclopropenium ions and four propargylic ions were derived.