Ion molecule reaction of a-phenylvinyl cation
m/z 196 indicate that the reaction product most likely has the
structure of the protonated p-alkenylanisole.
heteroatom of the substituent is bonded to alkyl groups, such as
in the case of anisole and N,N-disubstituted aniline, the attack
on the phenyl ring of the PVC occurs exclusively at the para posi-
tion. Significant product ions also appearing in the spectrum
correspond to the trans-vinylation reaction products [M + 25]+
which arise from the [M + 103]+ product ions via elimination of
the aromatic portion of the a-PVC.
Reaction with aniline (5) and N,N-diethylaniline (6)
The reaction of the a-PVC with neutral aniline generates the
product ion 5a at m/z 196 (Table 1). Upon CID, in addition to
.
the formation of the ions at m/z 181 (loss of CH3), m/z 118 (loss
of benzene) and m/z 103, the reaction product shows elimination
of NH3 (m/z 179) and of neutral phenylacetilene to yield proton-
ated aniline (m/z 94) (Fig. 5a). These behaviours provide evidence
for the structure of the protonated ring-alkenylated aniline for
the reaction products 5a, or, at least, for part of its population.
In particular, the loss of NH3 is a typical feature of the CI spectrum
of primary anilines.
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The higher intensity of ions at m/z 180 (100%), m/z 181 (60%)
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p-alkylated compound 21 (Fig. 5d), rules out the possibility that
the ring alkenylation occurred at the para position, supporting
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compound 20 (Fig. 5c) did not allow us to establish if, together
with ortho-alkylation, the attack occurred in some extent also
on the nitrogen atom.
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ortho-alkylated product ion 5a, we investigated the effect of the
N-substitution on the reaction with the phenylvinyl cation: we found
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gave only para alkylation. In fact, although the CID spectrum of the
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protonated 22 and 23, namely ortho- and para-alkylated N,
N-diethylanilines, respectively (Fig. 6b–c), however, the lack of ion
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We therefore supposed that the ortho-alkylation of a-PVC on
neutral aniline (6) proceeds throughout the same interaction ob-
served for phenol.
CONCLUSIONS
The a-PVC reacts selectively in a traditional ITMS with mono-
substituted benzenes bearing electron donating groups. The
typical reaction product consists in an alkenylated product ion
[M + 103]+ which shows a characteristic site of attack depending
on the nature of the substituent on the neutral molecule. The
reaction of PVC with phenol and aniline has shown, together with
direct substituent alkenylation, an unexpectedly large extent of
ortho alkenylation products. This result has been explained by
an interaction which involves the hydrogen of the hydroxyl/
amino group and the vinyl moiety of the a-PVC. When the
J. Mass. Spectrom. 2011, 46, 1115–1124
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