Premium
Substituent effects in mass spectra of monosubstituted benzils
Author(s) -
Richards Kenneth E.,
McMaster Blair N.,
Wright Graeme J.
Publication year - 1975
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.1210100408
Subject(s) - benzil , ion , chemistry , substituent , analytical chemistry (journal) , ionization , mass spectrum , spectral line , ionization energy , medicinal chemistry , organic chemistry , physics , astronomy , catalysis
The mass spectra of a series of thirteen m ‐ and p ‐substituted benzils have been determined at several ionising voltages below 20 eV and at 70 eV. At ionising voltages up to 5 eV above the ionisation potentials the benzil molecular ions decompose entirely by two pathways to give substituted and unsubstituted benzoyl ions. Fractional intensities of the molecular ion (F M ), substituted (F X ) and unsubstituted (F H ) benzoyl ions were obtained for each benzil as a function of energy from measured ionisation efficiency curves, and ionisation and appearance potentials for all major ions determined from the ionisation efficiency curves by a semilogarithmic method. Various correlations of ion intensity and energy parameters with δ + and δ constants are examined; these are generally poor. Fair correlations are obtained between log (F X /F H ) or (AP (XC 6 H 4 CO) +– AP (C 6 H 5 CO) +) and δ or δ + , and these are interpreted in terms of the expected effect of substituents on the stabilities of the product ions in the decompositions. A good correlation is observed between log (F X /F H ) and AP (XC 6 H 4 CO) +· AP (XC 6 H 5 CO) +; this suggests that substituents affect F X /F H mainly by changing the activation energies for the competing decompositions of the molecular ions. The competitive shift has a marked effect on these appearance potentials so that in this system AP – IP is not a good measure of the activation energy for the primary decompositions.