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Collisionally Activated Dissociation of Some Bulkily Substituted Pyridinium Cations, II. Substituent Effect on Appearance Potential
Author(s) -
Anders Ernst,
Koch Rainer,
Katritzky Alan R.,
Malhotra N.,
Eyler John R.,
Zimmerman Jeffrey A.
Publication year - 1992
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19921250129
Subject(s) - chemistry , pyridinium , carbocation , dissociation (chemistry) , substituent , pyridine , ion , molecule , computational chemistry , photochemistry , stereochemistry , medicinal chemistry , organic chemistry
Collisionally activated dissociations (CADs) of various pyridine‐ring substituted N ‐benzylpyridinium cations in the gas phase form the substituted pyridine and benzyl carbocation. Appearance energies ( AE s) are estimated quantitatively from the appearance thresholds of the corresponding fragment ion from the laser‐desorbed pyridinium cations. MO calculations predict that such unimolecular dissociation processes lead initially to ion‐molecule pairs (IMPs): some such IMPs are of significantly lower energy than the fully dissociated products. The AE s have also been compared with the energy differences [ΔΔ H f =Δ H f (Py) + Δ H f (R + ) — Δ H f (Py+R)] determined by AM1 calculations: in many cases these are quite close to the calculated energy differences; discrepancies are discussed.