Collisionally Activated Dissociation of Some Bulkily Substituted Pyridinium Cations, II. Substituent Effect on Appearance Potential

0009-2940

Gas-phase dissociation ; Appearance energies ; Calculations, AM1 ; Pyridinium cations, N-benzyl-2,4,6-substituted ; Chemistry ; Inorganic Chemistry

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

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 (AEs) 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 AEs have also been compared with the energy differences [ΔΔHf=ΔHf(Py) + ΔHf(R+)  -  ΔHf(Py+R)] determined by AM1 calculations: in many cases these are quite close to the calculated energy differences; discrepancies are discussed.

1 Ill.

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