A new general fragmentation reaction in mass spectrometry: The hydrogen-carbon, carbon-carbon double rearrangement of 2 heteroalkyl substituted diphenylmethyl cations

Studies in organic mass spectrometry. Part 25. Benzyl ion formation in chemical ionisation (methane or isobutane) of someortho-alkylhetero-substituted diphenylcarbinols

“…In order to ascertain whether the peak at m/z 91 of 1 and 2 corresponds to the rearrangement ion b (Scheme ), we examined the CI (methane) mass spectra of isotopomers 1d 3 and 2d 3 (Figs 1(b) and 2(b), respectively). The complete shift to m/z 93 confirms the formation of the ion b by the double rearrangement reaction of diphenylmethyl cations, previously observed in electron ionisation mass spectra 1–4. The peaks due to anisole loss, at m/z 107 and 121 for 1 and 2 , respectively, are not shifted in the spectra of the isotopomers 1d 3 and 2d 3 .…”

“…It has been reported that diphenylmethyl cations formed by the benzylic cleavage of the molecular ions of 1,1‐diphenylalkanes bearing, in the ortho position, an alkoxy, alkyl‐ or dialkylamino or alkylsulfanyl group undergo a double rearrangement process involving consecutively a H‐to‐C migration followed by a C‐to‐C displacement reaction1–4. The overall process affords benzyl (or tropylium) cations through migration of an alkylidene residue of the ortho ‐alkylhetero group to the other aromatic ring (Scheme ), and this constitutes a pathway for benzyl (or tropylium) cation formation not previously reported 5,, 6…”

Substituent effects on the formation of benzyl ions from ortho-methoxy substituted 1,1-diarylalkanes under electron ionization: correlations between the abundance of the process and the 13C-NMR chemical shifts of the neutral precursors

“…2,3 It has been unequivocally demonstrated by experiments with 2 H-and 13 C-labeled compounds that the whole process of benzyl ion formation involves migration of the methylene residue of the methoxy group linked to the 2-position of an aromatic ring (ring A) to the other aromatic ring (ring B). [1][2][3][4] Further investigation revealed that such a reaction occurs also for ortho-alkoxy derivatives (OEt, OiPr) by migration of an alkylidene residue other than methylene, as well as for ortho-alkyl-hetero (NHMe, NMe 2 , SMe) 1,1-diarylalkanes. 4 Finally, it has been determined that the formation of the benzyl-(or tropylium) ions b constitutes the main unimolecular decomposition reaction of ortho-alkylhetero-substituted diaryl-or alkyldiaryl-or triaryl-methyl cations, a, generated either under electron ionization 5 Step 1…”

“…[1][2][3][4] Further investigation revealed that such a reaction occurs also for ortho-alkoxy derivatives (OEt, OiPr) by migration of an alkylidene residue other than methylene, as well as for ortho-alkyl-hetero (NHMe, NMe 2 , SMe) 1,1-diarylalkanes. 4 Finally, it has been determined that the formation of the benzyl-(or tropylium) ions b constitutes the main unimolecular decomposition reaction of ortho-alkylhetero-substituted diaryl-or alkyldiaryl-or triaryl-methyl cations, a, generated either under electron ionization 5 Step 1…”

Kinetic study of base-promoted elimination reactions of some 1,1,1-trihalo-2,2-bis(dimethoxyphenyl)ethanes in alcoholic solutions

“…3 In contrast, the abnormally slow elimination of 2-(2,4,6-trinitrophenyl)ethyl bromide, which reacts at the same rate as the dinitro derivative, was attributed to steric effects that reduce the efficiency of the electron-withdrawing 2,4,6-trinitrophenyl group. 3 The interest in the properties of 1,1-diarylethanes 4 induced us to investigate the base-promoted elimination reaction of the bis(3,4-dimethoxphenyl) (lb), bis (2,5-dimethoxyphenyl) (1c). and bis(2,4-dimethoxyphenyl) (1d) derivatives 5 .…”