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Kinetic studies in mass spectrometry—VIII: Competing [M CH 3 ] and [M CH 2 O] reactions in substituted anisoles. Approximate activation energies from ioniziation and appearance potentals
Author(s) -
Brown Peter
Publication year - 1970
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210040153
Subject(s) - chemistry , substituent , cleavage (geology) , ion , kinetic energy , transition state , ionization , mass spectrometry , stereochemistry , computational chemistry , medicinal chemistry , catalysis , organic chemistry , physics , chromatography , quantum mechanics , geotechnical engineering , fracture (geology) , engineering
Ionization and appearance potentials have been determined for apparently competing [M CH 3 ] cleavage and [M CH 2 O] rearrangement reactions in a series of m ‐ and p ‐X substituted anisoles. Approximate activation energies AP–IP for most substituents are found not to differ by more than approximately 0.20 eV for m ‐ and p ‐X compounds with the same substituent. This finding implies either common rearranged molecular ions and/or transition states for the [M CH 3 ] and [M CH 2 O] reactions; or simply rather similar activation energies in unrearranged molecular ions. Assuming no rearrangment, we have found plots of AP–IP against σ + to give reasonable linear correlations of positive slope for both reactions. To account for this, it is suggested that in the activated complexes for both cleavage and rearrangement, an additional degree of positive charge is developed at the reaction site, and concordant mechanisms are proposed. These conclusions have been compared to those obtained by application of peak relative intensity methods such as Z‐values and their modifications.