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].
非8-烯酸根阴离子在碰撞激发下会失去C3H6、C4H8和C6H12的元素。通过产物离子和标记(2H和13C)研究以及中和重离子质谱研究,这些过程的机制得到了阐明。这些研究使我们得出以下结论:(i) C3H6的失去涉及非8-烯酸的烯醇阴离子的环化,生成环戊基羧酸根阴离子和丙烯。(ii) C4H8的损失是一个远程电荷过程(远离带电中心进行的过程),生成戊-4-烯酸根阴离子、丁二烯和氢分子。此过程与复杂的氢交换同时发生并相互竞争。(iii) C6H12的主要损失主要通过一个远程电荷过程进行,生成丙烯酸根阴离子、六烯-1,5和氢分子,但在此过程中没有氢交换伴随。(iv) 主要原因是这两个远程电荷过程优先于从相应的4-和2-阴离子中失去丁-1-烯和己-1-烯,尽管这些阴离子已形成,它们具有比失去丁-1-烯和己-1-烯更为替代且低能量的碎片化路径;即暂态的4-阴离子易于进行质子转移以生成更稳定的阴离子,而2-(烯醇)阴离子则更倾向于环化,随后排除丙烯[见上文(i)]。