Rearrangements, mass spectral

Similar mass-spectral rearrangements have been observed in sulphon-amides (66, 67), sulphonimides (68), and phosphine oxides (69, 70). 

An unusual formation of A-arylpyrroles was observed upon thermolysis of N-(4-aiylsulfenylbut-2-ynyl)anilines that was accompanied by elimination of a benzenethiol unit100. Mass-spectral rearrangements of A-propynylanilines and related compounds were studied more recently101,102. 

There are correlations between mass spectral fragmentations and thermal and photochemical fragmentations and rearrangements see Sections 4.02.1.2.1 and 4.02.1.2.2. 

McLafferty rearrangement (Section 12.3) A mass-spectral fragmentation pathway for carbonyl compounds. 

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

Dienes and polyenes show a pronounced molecular ion in the mass spectra and hence the molecular weight of polyenes can be determined by positive ion mass spectra. The easy removal of a 7r-electron from a diene is usually the reason for the distinct M +. The mass spectral investigation of conjugated polyenes is somewhat similar to that of aromatic structures, due to the high stability of the rearranged ions formed after the... 

Mass spectral analysis of thieno[2,3-h]thiophene (1) and thieno[3,2-ilthiophene (2) reveals skeletal rearrangement similar to that in... 

Extensive nuclear magnetic resonance and ultraviolet spectroscopy methods were reviewed in <1996CHEC-II(7)363>, as well as mass spectral fragmentation patterns of [l,2,3]triazolo[4,5-/ ]pyridines (Section 7.10.8.1). More recently, furoxan rearrangement of some pyridofuroxan derivatives has been studied by H, and... 

On reduction, spireine afforded di- and tetrahydro derivatives. The location of two keto groups in spireine was revealed by H-NMR and mass spectral analysis of deuterated spireine and tetrahydrospireine. When spireine was heated with selenium at 340°, a compound with molecular formula C20H27NO2 was obtained. Structure 182 was proposed for this compound on the basis of spectral data. Since the C-19 imine bond is usually unstable and cannot be isolated in that form, we suggest that the imine bond is present at C-20 rather than at C-19 in the selenium degradation product (C2oH27N02). Thus, structure 183 should be considered for the latter. Each of the structures considered for spireine has unusual features. The exocyclic double bond in 181 bears some resemblance to lycoctamone (184), a rearrangement product of lycoctonine. 

Unlike the model system, (66) could not be brominated directly. Therefore, it was converted into the ketone (67) by heating in 80% acetic acid, and this ketone was brominated with excess bromine in ether to give (68). Conversion of (68) into the acetal (69) was accomplished with diethylene orthocarbonate and toluene-p-sulphonic acid. Rearrangement of (69) to (70) was effected by heating with excess 1,5-diazabicyclo[3,4,0]nonene in xylene-DMSO. On comparison of i.r., n.m.r., and mass spectral data, this synthetic racemate was identical with the corresponding derivative from natural chasmanine. 

Further examples of the four-centre scheme may be seen in the mass-spectral fragmentations (86)-(88) in which aryl rearrangement is prominent. 

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