Trends in alkyl substituent effects on nucleophilic reactions of carbonyl compounds: Gas phase reactions between amines and the methoxy methyl cation

Eur. J. Mass Spectrom. 10, 233–238 (2004)
DOI: 10.1255/ejms.533

Trends in alkyl substituent effects on nucleophilic reactions of carbonyl compounds: Gas phase reactions between amines and the methoxy methyl cation

Lihn Bache-Andreassen and Einar Uggerud^*
Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway

ABSTRACT:

The reactions of various amines (RNH₂; R = H, CH₃, C₂H₅ andi-C₃H₇) with the methoxy methyl cation (CH₂OCH₃⁺) have been investigated using an FT-ICR mass spectrometer, and the experimental results are supplied with ab initio calculations. The amines show clear trends in their reactivities with variable degree of: 1) nucleophilic substitution, 2) addition-elimination and 3) hydride abstraction. In all cases addition–elimination dominates over nucleophilic substitution, and for R ≠ H the observed reactions occur at the collisional limit. The potential energy profiles for all three reaction types correlate with the basicities of the amines; the more basic amine—the more favourable is the reaction; in other words: nucleophilicity follows basicity in the gas phase.

Keywords: Mass spectrometry, quantum chemistry, physical organic chemistry, reaction mechanism, gas phase ion chemistry, reactivity, nucleophilic addition, nucleophilic substitution

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