THE MECHANISM OF PROPENE ELIMINATION FROM THE IMMONIUM IONS CH2=N+(CH3)CH(CH3)2 AND CH2=N+(CH3)CH2CH2CH3

It is shown by H-2-labelling experiments that beta-hydrogen transfer from the propyl group to the nitrogen atom is not an adequate general explanation for propene loss from CH2=N+(CH3)C3H, ions: beta-hydrogen transfer occurs for CH2=N+(CH3)CH(CH3)2, in which the N-alkyl substituent corresponds to a stable isopropyl cation; but alpha- and gamma-hydrogen transfer dominate for CH2=N+(CH3)CH2CH2CH3, in which isomerisation of the unstable incipient n-propyl cation precedes propene expulsion.