Effect of ortho substituents in the electron impact induced fragmentation of 2,2′‐disubstituted stilbenes

Abstract

The effect of ortho substituents NH,, OCH,, CH,, C1 and NO, on the fragmentation of five symmetrically and five unsymmetrically 2,2'-disubstituted stilbenes under electron impact was investigated. The fragmentation patterns deduced were supported by metastable transitions in the first and second field free regions and by exact mass measurements of prominent ions. In general, the fragmentation was found to be in accord with that of stilbene and the corresponding monosubstituted stilbenes. There are, however, some deviations from the general fragmentation scheme caused by direct through-space interactions of the ortho, ortho' substituents with concomitant loss of neutral fragments. It is supposed that the formation of 7-membered cyclic or heterocyclic ions is the result of such through-space reactions.

Isolation and tentative identification of compound in bleached‐kraft mill effluent capable of causing mixed‐function oxygenase induction in fish

“…As determined by high‐resolution mass spectrometry, the differences between the m/z 342 ion composition and the m/z 358 molecular ion indicated losses of both oxygen and methane. Each of these rearrangement processes (M + — 16) has been reported as a fragmentation pathway of ortho‐disubsti‐tuted methoxystilbenes [11]. The rearrangements occur through extrusion of oxygen, by methyl migration, to the eth‐ylenic bond and/or by direct expulsion of methane.…”

“…In most cases, the fluorenyl (m/z 165) and biphenylene (m/z 152) ion fragments are present in the spectra, but their use for confirmation here was negated by high levels of background ionization in this region. The elimination of the CH 3 Cl from ortho‐substituted methoxychlorostilbenes has been documented [11]. Tentatively, we postulate the active compound to be a chlo‐rination by‐product of one of the natural plant stilbenoids that are prominent in Pinus excelsa [14].…”

Mass spectral studies of diamide compounds obtained by the Ugi reaction

“…As was pointed out above, compounds 1 and 2 both possess two peptide-type bonds, named A and B. Their cleavages in EI and MS/MS processes show similarities to, as well as, major differences from the breaking of bonds in peptides, peptoids and retropeptides, [15] as well as remarkable differences and similarities between themselves. For example, cleavage of the A 0 bond leads to formation of the styryl fragment ion, a 1 , at m/z 103, while the x 2 fragments are neutral for both compounds.…”

“…In this sense, we and other authors have already reported similar rearrangements in the EI spectra of chalconoid and stilbene compounds. [7,[11][12][13][14][15] The high intensity of the peak at m/z 236 in the cis isomer discussed above could be attributable to the easier formation of the third ring in this isomer than in the trans one.…”

Tetramethylammonium hydroxide (TMAH) thermochemolysis of 2-arylcoumaran lignin model compounds

“…The m/z 165 fragment ion can be explained as the [(OMe) 2 C 6 H 3 CHbCH 3 ] + species, which is produced by the migration of the methyl radical of the 2-methoxyl group to the Cb atom of the central double bond of the stilbene (pathway 1) and successive cleavage of the Ca-Cb bond [20]. Similarly, the migration of the methyl hydrogen of the 2-methoxyl group to the Cb atom of the double bond (pathway 2) and successive cleavage of the Ca-Cb bond provide the m/z 151 ion due to the [(OMe) 2 C 6 H 3 CbH 2 ] + species [21].…”