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The role of ion–neutral reorientation in the unimolecular reactivity of e‐ionized amines. The influence of the size of the fragments
Author(s) -
Longevialle Pierre
Publication year - 1995
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1290091221
Subject(s) - chemistry , metastability , ion , decomposition , kinetic energy , reactivity (psychology) , dipole , homologous series , chemical physics , ionization , computational chemistry , crystallography , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics
During the unimolecular decomposition of an ion IN→I(ion) + N(neutral), the fragments may mutually reorient before decomposition, when the energy has reached the reorientation critical energy. After I‐N reorientation, I and N have only a very low probability of recombining into the original IN structure, but can only decompose (or occasionally follow a different reaction pathway, if thermochemically allowed). As a consequence, decompositions of metastable ions are irreversibly decided as soon as their corresponding I‐N reorientation threshold has been reached. It is shown, from the mass‐analysed ion kinetic energy of several series of homologous primary amines, that the competition between α‐cleavages (and the occasionally accompanying losses of alkanes) is governed by the relative I‐N reorientation–(rather than decomposition)–critical energies. When the neutral has no permanent dipole, the I‐N reorientation critical energy depends on the sizes of the fragments, especially that of the fragment ion. An interpretation is proposed related to the McAdoo and Hudson hypothesis. 27