UNSPECIFIED. (1993) UNIMOLECULAR REACTIONS OF ISOLATED ORGANIC IONS - REACTIONS OF THE IMMONIUM IONS CH2=N+(CH3)CH(CH3)2, CH2=N+(CH3)CH2CH2CH3 AND CH2=N+(CH2CH2CH3)2. JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2 (12). pp. 2363-2372. ISSN 0300-9580

Abstract

The reactions of metastable CH2=N+(CH3)C3H, immonium ions have been investigated by means of H-2-labelling experiments and kinetic energy release measurements. Loss of C3H6, with specific beta-H transfer, is the sole channel for dissociation of CH2=N+(CH3)CH(CH3)2. This process gives rise to a Gaussian metastable peak. The isomeric ion, CH2=N+(CH3)CH2CH2CH3, also expels C3H6; however, both alpha-H and gamma-H as well as beta-H transfer occurs in this case, and the reaction proceeds with an increased kinetic energy release. The role of ion-neutral complexes in C3H6 loss from CH2=N+(CH3)C3H7 ions is discussed. In addition, CH2=N+(CH3)CH2CH2CH3 eliminates C2H4. This fragmentation yields a broad dish-topped metastable peak, corresponding to a very large kinetic energy release (T1/2 approximately 73 kJ mol-1), and it involves specific and unidirectional gamma-H transfer. A potential energy profile summarising the reactions of CH2=N+(CH3) CH2CH2CH3 and CH2=N+-(CH3)CH(CH3)2 is constructed. The mechanisms by which immonium ions of this general class eliminate C3H6 and C2H4 have been further probed by studying the behaviour of the higher homologue, CH2=N+(CH2CH2CH3)2. The mechanistic conclusions derived from this work are found to be in excellent qualitative agreement with those of previous studies.

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