Thermochemistry of organic and heteroorganic species. Part IX. Photoionization studies of isomerization and fragmentation of polysubstituted cyclopropenes: phenyl-substituted cyclopropenes

Ionization and appearance energies of some fragment ions from 1,2,3-trimeth yl-3-phenyl-, 3-methyl-1,2,3-triphenyl-, 1,2-diphenyl-3-methoxycarbonyl-, 1 ,2,3-triphenyl-3-methoxycarbonyl- and 1,3,3-triphenyl-2-methoxycarbonyl-cyc lopropenes were measured by photoionization mass spectrometry, It was shown that in none of these compounds did the fragment ions possess the expected stable substituted cyclopropenium ion structure. Accordingly, possible sch emes of molecular ion isomerization are given. The enthalpies of formation of nearly 50 substituted cyclopropenium ions, and ions of related structure , were estimated using series of isodesmic reactions. This publication, tog ether with the previous works of the authors in this Journal, demonstrates the general methodology for estimation of the enthalpy of formation for eve n-electron ions. It is suggested that the present methodology can provide a good alternative to other estimation or computation procedures applied to the thermochemistry of ions.