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.     

An ESR on formation of iminoxy free radicals—solvent effect on hyperfine splitting constants

The solvent effect on hyperfine interaction in three different types of iminoxy radicals obtained by oxidation of di-2-pyridiketoxime (1), diethyl hydroxyimino(2-fluorophenyl)methanephosphonate (2) and isonitrosoacetophenone (3) have been analyzed. Linear correlations of hyperfine constants of ¹⁴N (both iminoxyl and pyridyl nitrogens of the iminoxyl derived from 1), ³¹P (isomer Z of the iminoxyl derived from 2) and ¹⁹F (both Z and E isomer of iminoxyls derived from 2 on E_T (30) solvent parameters have been found. Opposite directions of the dependencies for different nuclei of the same radical have been established. Anisotropic spectra of the radical derived from 1 and iminoxy radicals derived from -furildioxime have been obtained by γ-irradiation of solid oximes.     

Mass spectrometry of onium compounds—II. Carnitine and O-acyl derivatives

Carnitine and its O-acyl derivatives undergo two major pyrolytic reactions in the mass spectrometer. Firstly elimination of water from carnitine or acid from acylcarnitine takes place followed by intramolecular displacement and formation of crotonyl lactone and trimethylamine. Secondly intramolecular displacement occurs with formation of a substituted γ-lactone and trimethylamine. For the lower acid derivatives only the elimination pathway is important. For carnitine and higher derivatives both processes are important. The electron induced fragmentations of the major pyrolysis products are relatively simple. The most important pathways for the major components are discussed. The pyrolytic composition and mode of fragmentation are characteristic and can be used for identification purposes.     

Mass spectrometry of heterocyclic compounds—II: Electron-impact induced fragmentation of 3,5-diphenyl-1,2,4-oxadiazole

The electron-impact induced fragmentation of 3,5-diphenyl-1,2,4-oxadiazole has been investigated by labelling experiments, defocused metastable ion detections and high resolution mass measurements. The main fragmentation process suggests heterocyclic cleavage at the 1 to 5 and 3 to 4 bonds confirming our previous interpretation. The structure of the major fragment ion [C₇H₅NO]⁺· has been interpreted as being represented by the isomeric benzonitrile oxide and phenylisocyanate structures, the latter isomerising irreversibly from the former. The benzonitrile oxide structure is consistent with [C₇H₅NO]⁺· formation by cleavage of the 1 to 5 and 3 to 4 bonds.     

Mass spectrometry in cardenolide chemistry—I

The mass spectrum of penta acetyl gitoxin is reported and discussed. This cardenolide derivative has recently been the subject of extensive metabolic study. Fragmentation processes are described which account for all of the major ions. High resolution measurements, metastable peaks and mass shifts, for the propionyl derivative, are reported to establish the validity of these proposals. A brief indication of the potential value of this technique, when combined with deuteroacetylation, to metabolic studies in this field is given, along with comments on the spectra of related compounds.     

Mass spectrometry of organic compounds in the group V elements—II: Branched chain aliphatic derivatives

The behaviour of compounds I to XII under electron-impact (electron voltages 30 and 12 eV) was investigated. The abundance of the ions characteristic of amines was shown to decrease drastically with an increase of chain branching in alkylphosphines. Comparison of the spectra of VII and X led to the conclusion that the unshared electron pair of phosphorus does not affect the fragmentation. The main peaks in the spectra of phosphines corresponded to hydrocarbon fragments. The origins of the main fragment ions were confirmed by metastable peaks.     

Stability and equilibria of free radicals—III Preparation of stable, sterically shielded, diarylnitrogen radicals with donor and acceptor aryl groups in the same molecule

Diarrylamines ArNHAr′ (Ar = 2,4,6-tri-, 2,6-di- or 2,4-dinitrophenyl, and Ar′ = phenyl or a phenyl with electron-donating substituents) were prepared; their IR and UV spectra, electrooxidation and electroreduction potentials were studied. Oxidation of picryl- and 2,6-dinitrophenyl-substituted compounds with Ag₂O affords paramagnetic solution giving ESR signals with Ar′ has MeO or NR₂ substituents. Radicals IVi and Vi are stable even in crystalline state.     

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 spectra of indazolones and pyrazolones—II: 5-pyrazolones

The mass spectral fragmentations of 3-methyl-5-pyrazolone (I), 3-methyl-5-pyrazolone-1-d₁ (II), 3-methyl-5-pyrazolone-1,4,4-d₃ (III), 1-acetyl-3-methyl-5-pyrazolone (IV), 3-methyl-5-ethoxy-pyrazole (V), 3,4-dimethyl-5-pyrazolone (VI), 1,3-dimethyl-5-pyrazolone (VII), 1-acetyl-5-acetoxy-3,4-dimethylpyrazole (VIII), 1,2,3-trimethyl-5-pyrazolone (IX), 3,4,4-trimethyl-5-pyrazolone (X), 3,4,4-trimethyl-5-pyrazolone-1-d₁ (XI), 3-phenyl-5-pyrazolone (XII), 2-acetyl-3-phenyl-5-pyrazolone (XIII) and 5-acetoxy-3-phenylpyrazole (XIV) are reported. Comparison is made between the mass spectra of 5-pyrazolones and 3-indazolones. As for the latter compounds initial loss of ·N₂R is preferred to loss of ·CHO, and is followed by loss of CO. The [M ? 1]ions are intense in the C-methyl substituted pyrazolones, and unlike the 3-indazolones, the pyrazolones do not show any significant loss of HCN from these ions. The mass spectra distinguish between certain isomeric 5-pyrazolones.     

Mass spectra of 1,2,4-triazoles—II: Alkyl 1,2,4-triazoles

The mass spectra of monomethyl 1,2,4-triazoles contain fragment ions produced by specific cleavage of the heterocyclic ring. A major fragmentation from many molecular ions involves the elimination of HCN, but loss of N₂ is either very small or completely absent. No N or H scrambling occurs within the triazole ring system, as evidenced by labelling studies. The loss of a hydrogen atom from the molecular ions of 3-alkyl-1,2,4-triazoles (alkyl ? C₂H₅) originates from hydrogens attached to the β carbon and nitrogen atoms.     

The mass spectrometry of volatile derivatives—II: N-alkyl trifluoracetamides

Under electron-impact, N-alkyl trifluoracetamides exhibit peaks due to [CF₃]⁺ and [M ? CF₃]⁺. Ions corresponding to [COCF₃]⁺ are absent. The base peak in many straight chain derivatives occurs at m/e 126 due to alkyl radical loss from the molecular ion; the mass of this ion rising to m/e 140 in the α-substituted N-sec-butyltrifluoracetamide and to m/e 154 in the tert-butyl derivative. High resolution measurements on a number of peaks indicate that they originate by loss of HF from other fragment ions.     

Mass spectrometry in structural and stereo-chemical problems—CCXXIV: Fragmentation of cyclopropanes

Generalizations for interpreting the mass spectra of cyclopropanes are enumerated and are based on the examination of many deuterium labeled substrates. Most cyclopropyl fragmentations can be visualized as resulting from ionization of the most substituted cyclopropyl bond in which the positive charge is localized on the most substituted carbon atom. Subsequent hydrogen shifts and/or simple scissions produce an array of predictable fragment ions.     

High resolution mass spectrometry. Bufadienolides—II.

Complete low resolution mass spectra and high resolution data for selected important peaks are presented and discussed for a series of naturally occurring 14β, 15β-epoxybufadienolides (toad poisons) and their derivatives. The compounds examined were resibufogenin, marinobufagin, cinobufagin, desacetylcinobufagin, cinobufotalin, desacetylcinobufotalin and resibufagin, and the derivatives were 11α-hydroxyresibufogenin, 3β-acetoxymarinobufagin, 3-ketocinobufagin, 3β-acetoxy-16β-desacetylcinobufagin, 3β-acetoxy-16-ketocinobufagin, resibufaginol, 14α-artebufogenin and 3β-suberyloxyresibufogenin methyl ester. The relatively unsaturated 2-pyrone group of C-17β has been used as an integral label to distinguish (from elemental composition data) ions containing it from those arising in other parts of the molecule that do not, and the spectra are interpreted in terms of structural ‘ion types’.     

Mass spectrometry in structural and stereochemical problems—XXXIII Colchicine alkaloids

Mass spectra have been measured for a series of colchicine alkaloids and correlations between spectra and structure have been made. The results indicate that mass spectra will be of assistance in structure determination of such naturally occurring tropolones.     

Mass spectrometry of nitroazoles: 2—the mass spectra of methyl substituted nitroimidazoles

The mass spectra of six isomers of methylnitroimidazoles are reported and discussed. All compounds exhibit strong molecular ions, along with the characteristic fragmentations of aromatic nitro compounds. In some cases ortho effects—losses of OH^., H₂O, CHO^., CH₂O—are observed, due to interactions of adjacent substituents.     

Mass spectrometry of onium compounds—XI: Ionization potentials of hydroxy and mercapto pyridines

Ionization potential measurements of the volatile species from the three isomers of the tautomeric hydroxyl and mercapto pyridines show that these are in the hydroxy and mercapto forms rather than appearing as lactams and betaines. The corresponding N-methyl lactams and S- and O-methyl ethers were also studied for comparative purposes.     

Mass spectrometry of onium salts—I. Studies on anilinium oxides

The mass spectra of the three isomeric trimethylanilinium oxides and their methyl-d₃ analogues show that the m- and p- isomers undergo intermolecular trans-O-alkylation before evaporation. In the o-isomer, only 10% transalkylated product is observed and there is strong evidence that most of this isomer evaporates without undergoing structural changes. By indirect introduction, however, the o-isomer showed only transalkylated product. The most important fragmentation patterns on electron-impact are α-cleavage on the N-methyl carbon or expulsion of the O-substituent with formation of a quinoid structure. The latter dominates for the o- and p-methyl ethers while the former is the most important pathway for the m-isomer and for the corresponding phenols. Lower fragments are of modest intensity.     

Mass spectrometry in structural and stereochemical problems—CCXXIII:ortho interactions of nitro groups

The mass spectra of C¹³ labeled o- nitrobenzoic acid and o-nitrobenzaldehyde were studied. Earlier proposed fragmentations involving group migration to a charge-carrying vacant ortho position were verified. A completely unexpected interaction in o- nitroanisole was uncovered by O¹⁸labeling.     

First acetylenic derivatives of stable 3-imidazoline nitroxides

The Stephens-Castro reaction of copper(I) salts of 1-aryl(hetaryl)alkynes with 2,2,5,5-tetramethyl-4-[2-(4-iodophenyl)-vinyl]imidazoline-3-oxide-1-ol proved to be a general method for the preparation of 2,2,5,5-tetramethyl-4-[2-(p-aryl(hetaryl)ethynylphenyl)]vinyl-3-imidazoline-3-oxide-1-oxyles.