Mass spectral studies on steroidal compounds—V: Rings B and A seco 5-keto compounds in the cholestane series

The mass spectra of several structurally related ring B seco 5-keto compounds (I to VII) have been examined. The mass spectra of I, II, III and IV are conspicuous by an intense peak at m/e112(C₇H₁₂O) and those of V (highest mass peak at [M ? CH₃COOH]), VI and VII by a prominent peak at m/e 100 (C₇H₁₀O), which apparently results from McLafferty rearrangement involving 5-keto function and an appropriate γ-hydrogen at C-8 and C-11. This rearrangement, leading to the aforementioned ions, is of diagnostic value in the characterisation of such compounds. The mass spectrum of VIII exhibits a prominent ion peak at m/e 332 (C₂₃H₄₀O) resulting from McLafferty rearrangement involving the 5-keto function and C2? H. This offers an excellent means of differentiating between the isomeric acids (III and VIII). The fragmentation pathways suggested are supported by accurate mass measurement of the salient fragment ions and in some cases by appropriate metastable peaks.     

Mass spectral studies on steroidal compounds—I: Steroidal 6-one ethylene acetals

The mass spectra of several steroidal 6-one ethylene acetals have been examined. The spectra of I and II are conspicuous by an intense [M — 55] peak. This differentiates them from other acetals reported in the present study. The acetals III, IV, V, VI, VII and VIII show the expected behaviour related to the acetal IX. The fragmentation pathways suggested are supported by accurate mass measurement of the salient fragment ions and in some cases also by appropriate metastable peaks.     

Mass spectral studies on steroidal compounds. VIII—a comparative study of 6- and 7-oxalactones

The mass spectra of three steroidal ring B 7-oxalactones and one 6-oxalactone have been examined and comparison made with previously studied spectra of 6-oxa isomers. Whereas the mass spectra of 6-oxalactones are conspicuous by an intense peak at m/e 318, no such peak was found for 7-oxalactones. On the contrary, the 7-oxalactones showed characteristic [M ? CH₂O]⁺ ions. Thus, mass spectrometry offers an excellent means of differentiating between isomeric 6- and 7-oxa ?-lactones in the cholestane and β-sitostane series. The fragmentation pathways suggested are supported by accurate mass measurement of some of the salient fragment ions.     

Mass spectrometry of hop compounds—II: Mass spectra of related oxygen heterocyclic compounds

Mass spectra have been determined of a number of phloroglucinol derivatives and closely-related compounds encountered in chemical studies of hop components. Initial fission involving acyl, alkyl or alkenyl side-chains gives predominantly even-electron ions which then fragment their oxygen heterocyclic rings by elimination of neutral molecules, whilst gem-dialkenyl centres show preference for loss of an alkenyl group. The fragment ions induced by electron-impact may be correlated to a useful extent with molecular structure.     

The mass spectra of small-ring hetero-cycles—II. Aziridinones (α-lactams)

The mass spectra of six aziridinones (α-lactams) are presented. The six aziridinones exhibit the same general fragmentation pattern, the primary processes being loss of the N-t-butyl group, loss of carbon monoxide and loss of t-butyl isocyanate. Several additional rearrangement or fragmentation processes are observed with specific α-lactams.     

NMR spectral studies: XIII—titanium tetrachloride-induced and lanthanide-induced shifts in the proton NMR spectra of β-lactams

2-Azetidinones which carry a proton each on C-3 and C-4 often pose a problem in the correct assignment of the resonances due to these protons; titanium tetrachloride has been shown to be an effective and reliable n.m.r. shift reagent to differentiate between these two protons on the basis of their different sensitivities to this reagent. A few compounds were also studied with Eu(fod)₃ and Pr(fod)₃ for the sake of confirmation.     

NMR spectral studies. XIV. Carbon-13 nuclear magnetic resonance studies on β-lactams

Carbon-13 NMR spectra of a variety of mono- and bicyclic β-lactams have been measured and the chemical shifts of the ring carbon atoms have been assigned unambiguously. Effects of substituents on the chemical shifts of these carbons are also discussed.     

Mass spectral studies of unsaturated carboxylic acids—I: Some cyclic and acyclic βγ-unsaturated acids

The mass spectra of a series of βγ-unsaturated cyclic and acyclic carboxylic acids are reported. Metastable ion studies and precise mass measurements have been employed in demonstrating that the ten compounds studied conform to one or other of two generalised fragmentation pathways.     

Mass spectral studies on 7-azabicyclo (2.2.1) heptane systems

An attempt has been made to rationalise the major fragmentation modes of a few C₂, C₃ disubstituted 7-p-toluene sulphonyl and 7-carbobenzyloxy-7-azabicyclo (2.2.1) heptanes.