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 spectrometric studies of diterpenes: VIII—Epimers

Diterpene epimers differing with respect to orientation of a secondary hydroxyl group, ring fusion or configuration at an asymmetric centre carrying carbon–carbon linked substituents were studied, and certain stereostructural-spectral correlations were achieved for the first two groups. Each of the compounds examined was subjected to multiple scanning at both high and low electron voltage to allow computer assisted statistical calculation and comparison of intensity intervals at a predetermined confidence level for total ion currents and selected peaks.     

Mass spectral studies on steroidal compounds—II: 7a-aza compounds in the cholestane series (ring Bε-lactams)

The mass spectra of four structurally related 7a-aza compounds in the cholestane series have been examined. These spectra are conspicuous by the presence of a fragment ion peak at m/e 222 (C₁₅H₂₈N). which can be of diagnostic value in characterisation of such ε-lactams. The fragmentation pathways 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—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 spectrometry of natural products: VIII—Mass spectrometric studies of ring a saturated gibberellins

The fragmentation behaviour of gibberellin A₁ methyl ester and gibberellin C methyl ester has been studied by means of positive and negative ion mass spectrometry, high resolution techniques and metastable ion transitions. The results obtained allow a mass spectrometric distinction to be made between both structural types.     

Mass spectral studies of cycloheptatrienes. II—The monochlorocycloheptatrienes

The mass spectra of isomeric chlorocycloheptatrienes have been studied at high and low electron beam energies. Ion kinetic energy spectrometry was utilized to examine the major decomposition pathways. The extreme similarity found in the spectral characteristics of these compounds provides information about the structure of the decomposing molecular ion.     

Computer processing and interpretation of mass spectral information. VIII—ariadna system

The structure of a laboratory system for processing and interpreting mass spectral data intended to solve a wide range of analytical problems (determination of the composition and structure of molecules, isotopic analysis, etc) and research problems (study of the structure and reactivity of ions in the gas phase) is described and its functional possibilities are discussed. The basic software of the system includes both methods for calculation of elemental compositions of ions with the use of masses and amplitudes of isotopic peaks and methods for establishing spectralstructural correlations based on information theory and molecular graph theory.     

Mass spectra of steroidal alkyl ethers—I

The mass spectral fragmentation of saturated and unsaturated steroidal methyl and ethyl ethers and ethers of 4,4-dimethyl steroids are studied and compared to the fragmentation of steroidal alcohols, trimethylsilyl ethers and ethylene ketals. Unlike the trimethylsilyl ether the small fragment containing the alkoxy group is neither the base peak nor a very strong peak in the spectrum. A significant peak occurs at [M — ROH]^+·, however, sometimes even constituting the base peak of the spectrum. The fragmentations of the alkyl ethers are largely dependent on their environments. The present results also show the generalization that methyl ethers are better leaving groups than the corresponding alcohols in fragmentation processes, is not always valid.     

Linear solvation energy relationships VIII—solvent effects on NMR spectral shifts and coupling constants

The solvatochromic comparison method is used to unravel solvent polarity and hydrogen bonding effects on a variety of NMR spectral shifts and coupling constants. Solvent effects are rationalized in terms of the solvatochromic parameters π*, δ, α and β. Properties analyzed include ¹⁹F shifts of 5-fluoroindole, ¹H shifts of fluorodinitromethane, tert-butanol, phenol, 2-methylbut-1-en-3-yne, and thioacetamide, ¹H and ¹³C shifts and J(¹³C¹H) coupling constants of chloroform, ¹³C shifts of acetone, ¹⁵N shifts of pyridine, ¹⁵N and ²⁹Si shifts of 1-methylsilatrane, and some J(¹¹⁹Sn,C,¹⁹F) coupling constants of polyalkyltin compounds.     

Mass spectral fragmentation studies in usnic acid and related compounds

A study of the fragmentation patterns of the naturally occurring lichen substance, usnic acid (I) and various other chemically and biochemically derived compounds is reported and discussed. From these results it is demonstrated that the characteristic fragmentation patterns observed are of considerable utility in determining not only the substitution patterns on these highly oxygenated molecules, but also the structural elucidation of new compounds within the series.     

Mass spectral studies on aryl-substituted N-carbamoyl/N-thiocarbamoyl narcotine and related compounds

Positive ion mass spectral fragmentation of new N-carbamoyl/N-thiocarbamoyl derivatives of narcotine and compounds closely related to it are reported and discussed. The techniques used include electron impact (EI), fast-atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Prominent peaks in the mass spectra of these compounds appear to involve C-C bond cleavage beta to the amine nitrogen with loss of the 4,5-dimethoxy(1H)isobenzofuranone moiety from their molecular ions, along with another prominent peak at m/z 382. No molecular ion peaks of these compounds were recorded in EI, whereas intense [M + H]+ ion peaks were observed in FAB and ESI spectra. MALDI also yielded [M + H]+ ion peaks in good agreement with FAB and ESI studies.     

Mass spectral studies of unsaturated carboxylic acids. II—Some acids containing two double bonds

The mass spectra of some doubly unsaturated carboxylic acids are reported. Where C-2 is quaternary, the fragmentation pathway is similar to that previously demonstrated for βγ-unsaturated acids. The unbranched acids show different behaviour, similar to their thermal pyrolysis.     

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.     

Mass spectrometry of organic compounds of group V elements 7—N-alkoxyamines

The suggestion of participation of the participation Ione electron pair of the nitrogen atom in amine-type stabilization has been confirmed by a decrease in amine-type fragmentation and a drastic change in the decomposition routes under electron impact of N-alkoxyamines.