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Eur. J. Mass Spectrom. 6, 53 - 64 (2000)

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

V.V. Takhistov
Centre of Ecological Safety of Russian Academy of Sciences, 197042, St Petersburg, Korpusnaya 18, Russia
I.N. Domnin
Department of Chemistry, St Petersburg University, 198904, St Petersburg, Peterhof, University pr. 2, Russia
D.A. Ponomarev*
Department of Chemical Engineering, St Petersburg Forest Technical Academy, 194021, Institutski 5, St Petersburg, Russia

ABSTRACT:
Ionization and appearance energies of some fragment ions from 1,2,3-trimethy1-3-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-cyclopropenes 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 schemes 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, together with the previous works of the authors in this Journal, demonstrates the general methodology for estimation of the enthalpy of formation for even-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.

Keywords: photoionization, thermochemistry, aromatic ions

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