Premium
Unimolecular reactions of the isolated immonium ions CH 3 CH = NH + C 4 H 9 , CH 3 CH 2 Ch = NH + C 4 H 9 and (CH 3 ) 2 C = NH + C 4 H 9
Author(s) -
Bowen Richard D.,
Colburn Alex. W.,
Derrick Peter J.
Publication year - 1990
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210251005
Subject(s) - imine , chemistry , metastability , ion , hydride , fragmentation (computing) , medicinal chemistry , crystallography , stereochemistry , hydrogen , catalysis , organic chemistry , computer science , operating system
The reactions of ten metastable immonium ions of general structure R 1 R 2 CNH + C 4 H 9 (R 1 = H, R 2 = CH 3 , C 2 H 5 ; R 1 = R 2 = CH 3 ) are reported and discussed. Elimination of C 4 H 8 is usually the dominant fragmentation pathway. This process gives rise to a Gaussian metastable peak; it is interpreted in terms of a mechanism involving ion‐neutral complexes containing incipient butyl) cations. Metastable immonium ions ontaining an isobutyl group are unique in undergoing a minor amount of imine (R 1 R 2 CNH) loss. This decomposition route, which also produces a Gaussian metastable peak, decreases in importance as the basicity of the imine increases. The correlation between imine loss and the presence of an isobutyl group is rationalized by the rearrangement of the appropriate ion‐neutral complexes in which there are isobutyl cations to the isomeric complexes containing the thermodynamically more stable tert ‐butyl cations. A sizeable amount of a third reaction, expulsion of C 3 H 6 , is observed for metastable n ‐C 4 H 9 + NHCR 1 R 2 ions; in contrast to C 4 H 8 and R 1 R 2 CNH loss, C 3 H 6 elimination occurs with a large kinetic energy release (40–48 kJ mol −1 ) and is evidenced by a dish‐topped metastable peak. This process is explained using a two‐step mechanism involving a 1,5‐hydride shift, followed by cleavage of the resultant secondary open‐chain cations, CH 3 CH + CH 2 CH 2 NHCHR 1 R 2 .