Competitive charge-remote and anion-induced fragmentations of the non-8-enoate anion. A charge-remote reaction which co-occurs with hydrogen scrambling
Competitive charge-remote and anion-induced fragmentations of the non-8-enoate anion. A charge-remote reaction which co-occurs with hydrogen scrambling
作者:Suresh Dua、John H. Bowie、Blas A. Cerda、Chrys Wesdemiotis、Mark. J. Raftery、Julian F. Kelly、Mark S. Taylor、Stephen J. Blanksby、Mark A. Buntine
DOI:10.1039/a607437e
日期:——
The non-8-enoate anion undergoes losses of the elements of
C3H6, C4H8 and
C6H12 on collisional activation. The mechanisms of
these processes have been elucidated by a combination of product ion and
labelling (2H and 13C) studies, together with a
neutralisation reionisation mass spectrometric study. These studies
allow the following conclusions to be made. (i) The loss of
C3H6 involves cyclisation of the enolate anion of
non-8-enoic acid to yield the cyclopentyl carboxylate
anion and propene. (ii) The loss of
‘C4H8’ is a charge-remote process (one
which proceeds remote from the charged centre) which yields the
pent-4-enoate anion, butadiene and dihydrogen. This process co-occurs
and competes with complex H scrambling. (iii) The major loss of
‘C6H12’ occurs primarily by a
charge-remote process yielding the acrylate anion, hexa-1,5-diene and
dihydrogen, but in this case no H scrambling accompanies the process.
(iv) It is argued that the major reason why the two charge-remote
processes occur in preference to anion-induced losses of but-1-ene and
hex-1-ene from the respective 4- and 2-anions is that although these
anions are formed, they have alternative and lower energy fragmentation
pathways than those involving the losses of but-1-ene and hex-1-ene;
viz. the transient 4-anion undergoes facile proton
transfer to yield a more stable anion, whereas the 2-(enolate) anion
undergoes preferential cyclisation followed by elimination of propene
[see (i) above].