COMPETITIVE CHARGE-REMOTE AND ANION-INDUCED FRAGMENTATIONS OF THE NON-8-ENOATE ANION - A CHARGE-REMOTE REACTION WHICH CO-OCCURS WITH HYDROGEN SCRAMBLING

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 (H -2 and C-13) 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 ani on 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-enoa te anion, butadiene and dihydrogen. This process co-occurs and compete s with complex H scrambling. (iii) The major loss of 'C6H12' occurs pr imarily 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 charg e-remote processes occur in preference to anion-induced losses of but- l-ene and hex-l-ene from the respective 4- and 2-anions is that althou gh these anions are formed, they have alternative and lower energy fra gmentation pathways than those involving the losses of but-l-ene and h ex-l-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) a bove].