Rearrangements and fragmentations of phenyl styryl sulfides: 1—Metastable ion spectra

The mass spectra of two isomeric phenyl styryl sulphides show abundant peaks for fragment ions formed after interesting and unusual rearrangements, e.g. loss of CHS^˙ and C₇H₇^˙. Information about these rearrangements was obtained by comparison of the metastable peak intensities and peak shapes with those of four isomers. It appears that isomerization reactions between the phenyl styryl sulfides and the isomers are possible and that most of the metastable ion fragmentations proceed via reacting configurations that are common to two or more of the compounds investigated. The results indicate that an earlier proposed mechanism for the fragmentation of phenyl vinyl sulfides is incomplete and only partly correct for the compounds studied. Metastable ion spectra were obtained using high voltage scans and constant B/E scans: a short comparison of the results obtained with the two methods is given.     

Rearrangements and fragmentations of [C2H5S]+ ions

[C₂H₅S]⁺ ions (m/e 61) with different initial structures were generated in the mass spectrometer from twelve precursor ions. Abundance ratios of competing metastable ion decompositions were used to determine whether these ions decompose through the same or different reaction channels. It was concluded that all [C₂H₅S]⁺ ions isomerize to a common structure or mixture of structures prior to decomposition in the first field free region. From ¹³C labelling experiments it was concluded that [C₂H₅S]⁺ ions generated from the molecular ions of 2-propanethiol-2-[¹³C], partially rearrange to a symmetrical structure before decomposition to [CHS]⁺ and CH₄, whereas in [C₂H₅S]⁺ ions generated from the the molecular ions of 1,2-bis-(thiomethoxy-[¹³C]) ethane, the two carbon atoms become fully equivalent before CH₄ loss occurs.     

Rearrangements and fragmentations of [C2H5S]+ ions

From deuterium labelling experiments it was concluded that metastable molecular ions of ethyl methyl sulfide lose a methyl radical with the formation of both [CH₃S?CH₂]⁺ amd [CH₃CH?SH]⁺˙ The fragmentation reactions of metastable ions generated with these structure are losses of C₂H₂, H₂S and CH₄. These reactoins and the preceding isomerizations have also been studied by means of deuterium labelling. From the results it is concluded that the three fragmentation reactions most probably occur from ions with a C? C? S skeleton. Appearance energy measurements for ions generated with the two structures above and all give rise to the same ΔH_f value for these three isomeric forms. Ab initio molecular orbitals calculations confirm that these three ions fortuitously have very similar heats of formation. A potential energy diagram rationalizing the isomerizations and the principal fragmentation reaction is presented.     

N‐(p‐Chloro­phenyl)‐3,3‐di­phenyl‐4‐(β‐phenyl­styryl)azetidin‐2‐one

In the title compound, C₃₅H₂₆ClNO, the four‐membered β‐lactam ring is essentially planar, with a maximum deviation of 0.012 (1) Å for the N atom. The C—C bond lengths in the β‐lactam ring are 1.591 (2) and 1.549 (2) Å. The two phenyl rings attached to the β‐lactam ring are nearly perpendicular to each other [83.2 (1)°].     

Collisionally induced dissociative ionization of neutral products from ion fragmentations. 2—Collision gas effects and related phenomena

The ion retardation method (whereby an ion beam is prevented from entering a collision gas cell by means of a voltage applied thereto) for permitting the examination of the neutral products of unimolecular ion fragmentations has been extended to include observations of neutral products generated by collisions before the gas cell and their related phenomenology. Observations obtained using an ion beam deflection electrode, an alternative method of preventing the ion beam from entering the collision cell, are also reported. When low collision gas pressures are employed (<2×10^?7 Torr He), this latter method provides collisionally induced dissociative ionization (CIDI) mass spectra of unimolecularly generated neutral fragmentation products, free of complications arising from events induced by collisions occurring outside the collision cell. The CIDI mass spectra of CH₃˙, C₂H₄, CH₃?O, CH₃OH and C₂H₆ generated from positive ion precursors and CH₃˙, CH₃O˙ and C₆H₅NO₂ generated by electron loss from negative ions are described.     

Nitrogen-15 NMR studies of 1,4-benzodiazepines: 2—The triazolobenzodiazepines

Nitrogen-15 NMR data for a series of 21 triazolobenzodiazepines are presented, including ¹⁵N chemical shifts and substituent effects. The line assignments made by correlation to other model compounds were confirmed by a shift reagent and protonation study. A Yb(dpm)₃ study on alprazolam showed that the molar shifts of the four nitrogens ranged from 35 to 150 ppm.     

Metastable ion studies. III—composite metastable peaks in fragmentations of some small hydrocarbon cations

Composite metastable peaks are generated in the unimolecular fragmentations (i) [C₃H₅]⁺ → [C₃H₃]⁺ + H₂ (flat-top upon flat-top) and (ii) [C₄H₉]⁺ → [C₃H₅]⁺ + CH₄ (flat-top and gaussian). The measurement of appearance potentials and kinetic energy releases lead us to conclude, in agreement with earlier proposals, that in (i) the components can arise from the generation of the isomeric cyclopropenium and propargyl daughter cations. In (ii) the components are proposed to arise from the fragmentation of tert- and sec-butyl cations yielding allyl as the common daughter ion. The composite peak observed in the fragmentation (iii) [C₃H₄]⁺· → [C₃H₃]⁺ + H· is shown to be present only if the decomposing molecular ion is large enough to also produce [C₆H₈]²⁺ ions. The second component in (iii) then arises from the reaction [C₆H₈]²⁺ → [C₆H₆]²⁺ + H₂.     

Elucidation of elctron-impact-induced fragmentations of hydrocinnamaldehyde by 13C labelling; evidence for an ‘ortho attack’ in the molecular ion

The mass spectra of hydrocinnamaldehydes, labelled with ¹³C in Position 1 and 3, have been studied in order to determine the origins of the carbon atoms in the moieties C₂H₂O, C₃H₄O, CH₃ and CO, expelled from the molecular ion.     

4‐[3‐(3,4‐Di­methoxy­phenyl)­prop‐2‐enoyl]­phenyl methacryl­ate and 4‐[3‐(2‐bromo­phenyl)­prop‐2‐enoyl]­phenyl methacryl­ate

Chalcones (α,β‐unsaturated ketones) are effective antitumour agents. It has been proved that having halogen or methoxy groups substituted in various positions of the phenyl ring enhances the activity of chalcones many times. The title compounds, C₂₁H₂₀O₅ and C₁₉H₁₅BrO₃, respectively, were chosen for crystallographic study in order to determine their structures and conformations. In both compounds, the keto group is in the s‐cis conformation and is almost planar. There are weak intramolecular interactions in both structures.     

Preparation and synthetic utility of cyclopropyl phenyl sulfides

Primary alkyl halides and epoxides react with 1-lithiocyclopropyl phenyl sulfide to give derivatives suitable for transformation to carbonyl compounds or for desulfurization.     

Do­decyl 2‐nitro­phenyl disulphide

Do­decyl 2‐nitro­phenyl disulphide, C₁₈H₂₉NO₂S₂, contains an intramolecular S?O contact of 2.623 (3) Å. The angle between the planes of the NO₂ group and the attached phenyl ring is 4.2 (3)°. The thermal vibrations of the atoms increase along the paraffinic chain. The nitro­so O atom not involved in the S?O intramolecular contact also has high thermal motion. Attempts to create disordered models to allow for the thermal motions were unsuccessful.     

Nucleophile-assisted racemisations of halosilanes — kinetic studies

Kinetic studies have been carried out on the nucleophile-induced racemisation of PhMeCHSiMe₂X, 2, X = triflate, Br or Cl. Thirteen nucleophiles were studied. The results are interpreted in terms of two competing mechanisms for racemisation: (a) nucleophile attack on a silane-nucleophile complex formed by displacement of the halide by the nucleophile, and (b) halide-halosilane exchange, with inversion of configuration. Solvent effects were examined, and kinetic orders in the nucleophile and in one case for the halosilane were determined. The order in added nucleophile varied between one and two, with strong nucleophiles in polar media. Anomalously high orders in nucleophile were observed in non-polar media and are ascribed to aggregation of the nucleophile. A kinetic analysis of the competing mechanisms was attempted, and was consistent with the experimental findings. In this particular series of reactions involving compounds with good leaving groups and relatively powerful nucleophiles there was no evidence for intermediates involving extracoordinate silicon.     

Gas-phase NMR studies of chemical equilibria: 1—Methodology

Methods for obtaining ¹H NMR spectra of gases are discussed. Particular attention is paid to the nature of the tube and to the use of ‘second sample’ field/frequency locking. The question of the chemical shift reference is examined, and some results for tetramethylsilane gas are presented. Representative spectra are shown for three types of organic equilibria in the gas phase: keto-enol tautomerism, addition of methanol to acetaldehyde and Z-E isomerism of acetaldoxime.     

Halogenation of dichloro- and dibromovinyl(phenyl) sulfides

Bromination of 2,2-dichlorovinyl(phenyl) sulfide with bromine afforded a product that, upon heating or addition of zinc, cleaved the bromine to form the original sulfide. Chlorination of 2,2-dibromovinyl(phenyl) sulfide with chlorine resulted in substitution of a bromine atom by chlorine and/or hydrogen at the double bond as well as cleavage of the C-S bond to form polyhaloethenes, polyhalosulfides, and chlorinated dithioethenes. The chlorine addition product was absent.Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk 664033. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 955–957, April, 1992.     

Photoisomerization of trans‐2‐[4′‐(Dimethylamino)styryl]benzothiazole

Photoreaction of trans‐2‐[4′‐(dimethylamino)styryl]benzothiazole (t‐DMASBT) under direct irradiation has been investigated in dioxane, chloroform, methanol and glycerol to understand the mechanism of photoisomerization. Contrary to an earlier report, isomerization takes place in all these solvents including glycerol. The results show that restriction on photoisomerization leads to the increase in fluorescence quantum yield in glycerol. The results are consistent with the theoretically simulated potential energy surface reported earlier using time‐dependent density functional theory (TDDFT) calculations. DFT calculations on cis isomers under isolated condition have suggested that cis‐B conformer is more stable than cis‐A conformer due to hydrogen‐bonding interaction. In the ground state, cis‐DMASBT is predominantly present as cis‐B. The fluorescence spectra of the irradiated t‐DMASBT suggested that photoisomerization follows not the adiabatic path as proposed by Saha et al., but the nonadiabatic path.