Electron impact studies—LXVII. The mass spectra of alkyl-1,3-dithianes

The mass spectra of 1,3-dithiane, 2-methyl- and 2,2-dimethyl-1,3-dithiane have been studied by ²H labelling and metastable defocusing. The various molecular ions eliminate S₂H. to produce the ions [C₄H₇]⁺, [C₅H₉]⁺ and [C₆H₁₁]⁺ respectively, each of which scramble the hydrogens either before or accompanying further decomposition. Other processes are complex, but parallel those already reported for 2-aryl-1,3-dithianes.     

Electron impact studies—LXV: Negative-ion mass spectrometry of functional groups 2-aryl-1,3-dithianes

The negative-ion mass spectra of 2-aryl-1,3-dithianes contain pronounced molecular anions together with fragment ions which are produced by both simple and complex cleavage reactions. These spectra contain further examples of specific hydrogen scrambling processes in negative ions. Nitroaryldithianes give intense negative-ion spectra, and that of the o-nitro derivative exhibits an unusual proximity effect. The fragmentation patterns have been examined using both ²H and ¹³C labelling and the metastable defocusing technique.     

Electron-impact studies—L: Skeletal-rearrangement fragments in the mass spectra of diphenylpyrazoles and -isoxazoles

The mass spectra of all diphenylpyrazoles and -isoxazoles contain rearrangement peaks at m/e 165 [C₁₃H₉]⁺. In addition, the spectra of 3,5-diphenylisoxazoles contain peaks at m/e 180 [C₁₃H₁₀N]⁺, which are produced by specific phenyl migrations. The mechanisms of both rearrangement processes have been studied by deuterium labelling.     

Chemical ionization and electron impact mass spectra of alicyclic substituted 2-aryl-1,3-dithianes

The methane and isobutane chemical ionization mass spectra of alicyclic substituted 2-aryl-1,3-dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.     

2-aryl-1,3-dithianes and -dithiolanes: A nearly ideal series for relating the energies for bond breaking to electron transfer

By virtue of the stabilizing effect of the 1,3-sulfur atoms on the carbocations, radicals, and carbanions generated from the title compounds, it has been possible to measure a variety of bond-making and bond-breaking processes in the two very similar solvents, DMSO and sulfolane, and relate them to electron-transfer energies obtained by electrochemical techniques. Important properties reported from this and previously published work are as follows: heats of hydride transfer to the cations from cyanoborohydride ion, pK in aqueous acid, heats of deprotonation by K⁺ DMSYL/DMSO, pK_HA, redox potentials for the cations, and carbanions, which relate their energies to their conjugate radicals and to each other. The results support our previous assertion that the electron-transfer energy between the three trivalent oxidation states of carbon and the Parr-Pearson absolute hardness, ϵ, derived from it are the fundamental properties that determine energies for making and breaking two-electron bonds and thus determine most of organic chemistry. Excellent correlations are found for the substituent effects on energy changes associated with the various processes for making and breaking bonds to the cations, radicals, and carbanions and the electron-transfer energies for interconverting them. Many comparisons can be made with the corresponding 2-aryl-1,3-dioxo systems. Careful “bookkeeping” of these energies through appropriate thermochemical cycles shows excellent consistency despite a small solvent effect for transferring the ions from sulfolane to DMSO. Direct reaction of the carbocation with the carbanion of 2-phenyl-1,3-dithiane produced a clean formation of the dimer from which the heat of heterolysis (40.6 kcal/mol) and homolysis (19.1 kcal/mol) could be calculated. AM1 structures and heats of formation of two neutral species and two cations, a radical and an anion, have been computed and are generally consistent with stabilizing interactions of the gem sulfurs with the reactive center. The present study is the first, to our knowledge, to provide a coordinated view of the energies for generating the carbocations, radicals, and carbanions from a series of heterocycles. These energies are related to each other and to the electron-transfer energies for interconverting these reactive trivalent forms of carbon. © 1996 John Wiley & Sons, Inc.     

Electron-impact studies—LXX. Substituent effects in the negative-ion spectra of nitroaryl esters

The negative-ion mass spectra of a variety of substituted nitroaryl benzoates and aryl nitrobenzoates have been studied. Pronounced proximity effects are observed in the spectra of ortho-substituted compounds. The meta and para pairs fragment in a similar manner. Linear plots are observed for many cleavages using either the McLafferty or Harrison methods. Evidence is provided which suggests that the fragmentations of meta and para isomers may proceed by the same mechanistic pathway. The magnitude of ρ does not appear to provide precise information concerning the nature of the transition state for a particular reaction of a negative ion.     

Electron-impact studies—LIV: The formation of [C13H9]+ in the mass spectra of benzyl phenyl ketoxime and 2,3-diphenyl-2-H-azirine

The formation of m/e 165 in the spectrum of benzyl phenyl ketoxime involves the intermediacy of a rearranged 2,3-diphenyl-2-H-azirine radical ion. ²H and ¹³C labelling of the ketoxime together with ²H labelling of the azirine has allowed certain proposals to be made concerning the complex processes producing m/e 165 in both spectra. The mode of formation of m/e 167 in the spectrum of benzyl phenyl ketoxime has also been studied.     

Electron impact mass spectrometry of some 2-methyl-2-aryl- and 2-methyl-2-alkyl-1,3-dithianes

The electron impact mass spectrometric behaviour of four 2-methyl-2-aryl- and two 2-methyl-2-alkyl-1,3-dithianes is described and discussed in detail, with the aid of exact mass measurements, linked scans and mass-analysed ion kinetic energy spectrometry. The mechanism of the primary HS₂˙ loss, as well as those of the more unusual fragmentation pathways, are given.     

Electron-impact studies—LXXIV: A survey of rearrangement processes in the ‘doubly-charged ion’ mass spectra of aromatic compounds

The technique of Beynon² has been used to determine the ‘doubly-charged ion’ mass spectra of a variety of aromatic compounds which contain pronounced rearrangement peaks in their conventional mass spectra. Many, but not all, of the ‘doubly-charged ion’ spectra contain similar rearrangement peaks to those observed in conventional spectra.     

Electron-impact studies—LI: Hydrogen randomization in the stilbene molecular ion

Hydrozen randomization precedes the formation of M^+· ? H· and M^+· ? CH₃· species from the stilbene molecular ion at 15 eV. The carbon atom involved in the M^+· ? CH₃· elimination originates randomly from the whole molecule. The [M ? 15] ion (m/e 165) in the spectra of stilbene and 9,10-dihydrophenanthrene is produced from a common ion.     

Electron-impact studies—XVIII. Fragmentation of some epimeric 7-substituted norbornenes

The fragmentation modes of some epimeric 7-substituted norbornenes have been established from deuteration and high resolution studies. Stereochemical differences were found to have very little influence in directing the fragmentation modes of these epimers. Formation of common intermediates or transition states by ring opening process has been proposed to rationalise the mass spectral behaviour of these compounds.     

Electron-impact studies—LV: Skeletal rearrangement and hydrogen scrambling processes in the positive and negative-ion mass spectra of phenyl derivatives of elements of group IV and V

The mass spectra of many triphenyl/tetraphenyl derivatives of the Group IV and V elements exhibit the processes [M⁺˙ ? C₁₂H₁₀] and/or [M⁺˙ ? C₆H₅· ? C₁₂H₁₀]. These fragmentations are not preceded by hydrogen scrambling between all the phenyl rings. Hydrogen scrambling does occur in certain fragment ions prior to fragmentation in both the positive and negative-ion spectra. The process [M⁺˙ ? C₁₂H₁₀] occurs in the negative-ion mass spectrum of tetraphenylsilane.     

Simple and efficient deprotection of 1,3-dithianes and 1,3-dithiolanes by copper(II) salts under solvent-free conditions

Aerobic solid state deprotection of 1,3-dithianes and 1,3-dithiolanes of aromatic and aliphatic aldehydes and ketones has been performed in excellent yields by Cu(NO₃)₂·2.5H₂O in the presence of montmorillonite K10 clay and sonic waves at room temperature. These dethioacetalizations proceed more slowly but efficiently under catalytic conditions by using 20% of the copper(II) salt with K10 clay and sonication.     

Synthesis of 1,3-dithianes and 1,3-dithiolanes. Baker's yeast reduction and lipase-catalyzed resolution for synthesis of enantiopure derivatives.

Three 1,3-dithiolanes and four 1,3-dithianes have been synthesised from 1-(1,3-dithiolan-2-yl)-2-propanone and 1-(1,3-dithian-2-yl)-2-propanone, respectively. Asymmetric reductions of these ketones using baker's yeast gave the corresponding enantiopure (S)-alcohols. Baker's yeast also reduced the double bond in 3-(1,3-dithian-2-yl)-3-buten-2-one enantioselectively to give (S)-3-(1,3-dithian-2-yl)-2-butanone. 3-(1,3-Dithian-2-yl)-3-buten-2-one was also reduced chemo-selectively and the resulting 3-(1,3-dithian-2-yl)-3-buten-2-ol was resolved by transesterification in organic solvent using lipase B from Candida antarctica to yield the (S)-alcohol and the (R)-acetate with very high enantiomeric ratio, E. Racemic 1-(1,3-dithiolan-2-yl)-2-propanol and 1-(1,3-dithian-2-yl)-2-propanol were also resolved under similar conditions to give the (S)-alcohols and the corresponding (R)-acetates.     

Stereochemical studies—XXXVII: Saturated heterocycles—XIII Configuration and conformation of Z- and E-N-methyl- and -N- benzyl-2-p-nitrophenyl-4,5- and -5,6-tetramethylenetetrahydro-1,3-oxazines

The configuration and conformation of Z- and E-N-methyl- and -N-benzyl-2-p-nitrophenyl-4,5-, and -5,6-tetramethylenetetrahydro-1,3-oxazines were determined by ¹H and ¹³C NMR spectroscopy. The Z isomers were proved to be conformationally homogeneous, having the heteroatom in axial and equatorial position, respectively, in the case of the 5,6- and 4,5-tetramethylene compounds. Consequently, the p-nitrophenyl group and the anellated cyclohexyl ring are all-cis arranged in the Z-5,6-tetramethylene compounds while in the case of the Z-4,5-tetramethylene isomers the p-nitrophenyl group and the cyclohexyl ring are trans arranged to the hetero ring.     

Chemical ionization mass spectrometry studies—VII: Deuterium labeled decanes

CI mass spectra of the five isomeric vicinal d₂-decanes have been recorded using methane and d₄-methane as reagent gases. In contrast to earlier suggestions, we find that a large fraction of the alkyl fragment ions from n-decane are formed by elimination of olefins from the abundant [M – 1] ion. Only the C₉ and C₈ fragment ions are produced completely by a one-step reaction between the decanes and the methane reagent ions. Isotope exchange does not occur between the hydrocarbon and the reagent ions derived from d₄-methane but extensive scrambling of the deuterium label in the d₂-decanes does take place in the [M – 1] ion.     

Electron-impact studies. LXXXVII—ortho effects in the negative ion mass spectra of salicylates and anthranilates

The molecular anions of the methyl and phenyl esters of 4-nitrosalicylic acid and 5-nitroanthranilic acid eliminate ROH (R ? Me or Ph) by an ortho rearrangement. The molecular anions of phenyl 3-hydroxy-5-nitrobenzoate and phenyl 3-amino-5-nitrobenzoate lose PhOH to a lesser extent, and a study of the pressure dependence of these eliminations indicates the operation of simultaneous two-stage cleavage reactions. The competitive ortho effects observed when the nitro group is adjacent to either the ester or hydroxyl functions are described.     

Pmr spectra and stereochemistry of chiral 2-aryl- and 2-hetaryloxazolidines-1,3

PMR spectra of 2-aryl- and 2-hetaryloxazolidines-1,3 are studied. A PMR criterion is revealed according to which the absolute configuration of the C₍₂₎ atom of the oxazolidine ring can be assigned.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 678–680, May, 1992.