Mass spectra of trimethylsilyl derivatives of naturally occurring flavonoid aglycones and chalcones

Electron impact mass spectra of the trimethylsilyl derivatives of a series of flavonoid aglycones and chalcones are reported. The spectra show prominent ions arising from fragmentation of the trimethylsilyl (TMS) groups. Inter-actions between adjacent TMS groups, and between TMS groups in the 3- or 5-position (6′-position for the chalcones) and the C-ring carbonyl, yield structurally significant ions. Few fragments associated with the retro-Diels-Alder cleavage of the C-ring characteristic of the underivatized compounds, are observed. The TMS derivatives thus provide complementary information for the identification of flavonoid aglycones and chalcones in biological systems.     

The mass spectra of some N-substituted barbitals and their trimethylsilyl derivatives

The mass spectra of N-propyl and N-butyl barbitals show the loss of olefin radical (C_nH_2n-1) in analogy to structurally similar molecules such as N-alkyl succinimides and 3-alkyl uracils. Trimethylsilylation of the N-substituted barbitals suppresses this fragmentation and loss of olefin via apparent McLafferty rearrangement from the even-electron ion, [M – 15]⁺, becomes significant. The trimethylsilyl derivatives of N-allyl barbital and N-phenyl barbital show an unusually facile elimination of the appropriate isocyanate from the molecular ion.     

Synthesis of some naturally occurring prenylated juglone derivatives

Synthesis of -caryopterone (I), -dihydrocaryopterone )II), 9-methoxy--lapachone (III) and 4,9-dihydroxy--lapachone (IV) has been carried out starting from juglone via 2,8-dihydroxy-1,4-naphthoquinone.     

Mass spectra of some thioamide vinylogues and of their thiopyran derivatives

The analysis of metastable ions which decompose in the second field free region of a reversed geometry double focusing mass spectrometer is used to study the fragmentation of a series of thioamide vinylogues and their thiopyran derivatives. The fragmentation processes are discussed and the expected occurrence of an electron impact-induced retro-Diels-Alder reaction is confirmed.     

Mass spectra of some neopentylphosphorus derivatives

The fragmentation patterns and major metastable ions of the mass spectra of the neopentyl-phosphorus derivatives [(CH₃)₃CCH₂]₃P, [(CH₃)₃CCH₂]₂P(O)H, [(CH₃)₃CCH₂]_nPX_3-n (n = 1 and 2; X = H, Cl, C₆H₅ and CH = CH₂), [(CH₃)₃CCH₂]₃PS, [(CH₃)₃CCH₂]_nP(S)R_3-n (n = 1 and 2; R = C₆H₅ and CH = CH₂), [(CH₃)₃ CCH₂]₂PCH₂CH₂P[CH₂C(CH₃)₃]₂, ([CH₃)₃CCH₂]₂PCH₂PCH₂-CH₂P(H)C₆H₅ and [(CH₃)₃CCH₂]₂PCH₂CH₂P(S)(CH₃)₂ are described. Fragmentation of a neopentyl group by elimination of either C₄H₈ or CH₃ is very favourable when the neopentyl group is bonded to either a tricoordinate or tetracoordinate phosphorus atom. In neopentylphosphines with two or three neopentyl groups, stepwise elimination of C₄H₈ from all of the neopentyl groups occurs very readily. The resulting [(CH₃)_nPX]^+._3-n ions are often the most intense ions in the mass spectra.     

Mass spectra of some oxadiazole derivatives

The mass spectra of some substituted oxadiazoles have been determined and analysed with the aid of high resolution mass spectrometry. Some characteristic and major differences between their spectra have been noted, and possible rationalizations have been advanced. The main fragmentation patterns of the 1,3,4-oxadiazole derivatives have been interpreted in terms of diazirine intermediates. Specific skeletal rearrangement processes have been observed in the spectra of the 1,3,4- and 1,2,4-oxadiazoles, and possible mechanisms are proposed.     

The mass spectra of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives

The mass spectra of a series of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives have been determined. Fragmentation mechanisms are supported by high resolution, deuterium labeling and metastables.     

Mass spectra of some derivatives of amorphigenin

Conclusions The mass spectra of seven rotenoid compounds have been studied. The appearance of the main fragments in the mass spectra of the rotenoid is due to the cleavage of the bonds of the -pyrone ring. The molecules of the 7,8-dehydro-derivatives are more stable to electron impact.     

Mass spectra of some 4,5-dihydroimidazole derivatives

The mass spectra of a series of 4,5-dihydroimidazole derivatives were determined. Deuterium labelling and high resolution mass spectrometry were utilized in order to elucidate the mechanism of a number of fragmentations. The most significant ions arise from the following processes: (1) elimination of the C-4 substituent; (2) cleavage of the 1,2-N? C and 4,5-C? C bonds with or without hydrogen migration; (3) cleavage of the 1,5-N? C and 2,3-C? N bonds with charge retention on the N-1? C-2 moiety.

1 In this paper the standard numbering of the imidazole ring (see structures) is retained for the fragment ions.

Anomalous behaviour is shown by the t-butoxy derivative; the reasons for this behaviour are discussed.     

Mass spectra of some tropane and tropidine derivatives

Fragmentation patterns of tropane and tropidine derivatives have been shown to depend on the nature of the substituents. Unsaturation in the 6-membered ring leads to preferential fragmentation of the two carbon bridge. When the 6-membered ring is saturated and substituted with poor leaving groups (OH and CN) fragmentation of the 6-membered ring is preferred.     

Mass spectra of some 1,2,4-triazole derivatives

Fragmentation of various 1,2,4-triazole derivatives occurs by two predominant pathways involving the loss of RCN originating from both C₃ and C₅ positions. The resulting diazirinium radical cation was observed to lose a nitrogen atom to give a nitrilium ion whose substitution pattern was dependent upon the original substituents in the nucleus.     

13C nuclear magnetic resonance spectra of some naturally occurring friedelanones

¹³C NMR spectra of friedelan, friedelan-21-one, friedelan-6-one, friedelane-321-dione, friedelane-3,6-dione and friedelane-3,6,21-trione have been recorded and signals assigned using off-resonance decoupling, inversion recovery and lanthanide induced shift techniques.     

Mass spectrometry of the trimethylsilyl derivatives of some cardiac aglycones and monoglycosides

Mass spectra of the trimethylsilyl (TMS) ethers of digitoxigenin, digoxigenin, digitoxigenin monodigitoxoside, digoxigenin monodigitoxoside and peruvoside were obtained. Ions appearing at m/e 170 and m/e 183 are proposed to be indicative of the enol TMS ether moiety as confirmed by appropriate shifts in the mass spectrum of digitoxigenin derivatized with perdeuterotrimethylsilylating reagent. The TMS ether derivatives of the monoglycosides produced abundant molecular ions and the base peaks in the spectra represent fragments of the sugar portion of the molecule.     

Mass spectra of some derivatives of O-toluenesulphonic acid

The mass spectra of the derivatives of o-toluenesulphonic acid show a significant interaction of methyl and SO₂R groups. The change of a substituent mainly influences the decomposition mechanism of molecular ions and some fragment ions which are formed from them.¹     

The mass spectra of the trimethylsilyl derivatives of some alkyl and aminoalkyl phosphonates

The mass spectra of the trimethylsilyl derivatives of a series of alkyl and aminoalkyl phosphonates were investigated with the aid of deuterium labeling and high resolution mass measurements. The spectra contained several prominent ions characteristic of the phosphonate system and a number of ions produced by inter and intra molecular migration and interaction of trimethylsilyl groups.     

若干全氟环烃及其衍生物的拉曼光谱

由于C—F键的强极性,其振动模式在红外光谱中表现为强吸收谱带,而在拉曼光谱中则较弱,因此早期关于有机氟化合物振动光谱的研究以红外光谱为多,这方面Brown和Morgan已有详细总结.但有机氟化物的某些骨架振动往往呈现强的拉曼谱带.近年来对环状有机物的拉曼光谱研究已有较全面的总结,但对全氟环烷类及其衍生物尚无较系统的研究.本文报道若干全氟环烃及其衍生物的拉曼光谱数据,讨论了环呼吸振动频率与环大小及取代基的关系,环内双键振动频率的特性.实验证明全氟环烃的某些光谱特征与碳氢的环烃有较大的差异.