Fragmentation of pyrazolecarbaldehyde thio- and dithioacetals under electron impact and chemical ionization

The mass spectra of 1-substituted 3,5-dimethyl-1H-pyrazole-4-carbaldehyde bis(2-hydroxyethyl) dithioacetals and thioacetals were studied for the first time. The main fragmentation pathways of their molecular ions generated under electron impact and chemical ionization were similar. Primary decomposition of the molecular ions of bis(2-hydroxyethyl) dithioacetals involves elimination of 2-sulfanylethanol molecule with formation of the corresponding 1,3-oxathiolane radical cation. Fragmentation of the molecular ions [M]⁺ · and [M + H]⁺ derived from 2-(3,5-dimethyl-1H-pyrazol-4-yl)-1,4,6-oxadithiocanes includes cleavage of the eight-membered heteroring and elimination of C₄H₉OS ·. Substituents in the heteroring of pyrazolecarbaldehydes inhibit decomposition processes related to the aldehyde group.     

Mass Spectra of New Heterocycles: XIX. Electron Impact and Chemical Ionization Study of 2,7-Dihydrothiopyrano[2,3-b]pyrrol-6-amines

Russian Journal of Organic Chemistry - Fragmentation of N, N-dialkyl-7-[alkyl and 2-(vinyloxy)ethyl]-2,7-dihydrothiopyrano[2,3-b]pyrrol-6-amines under electron impact (70 eV) and chemical...     

A new approach to the synthesis of strained cyclic systems: II. Mass spectrometric study of 2-dialkylamino-3-phenylthiophenes and their structural isomers, iminothietanes and iminocyclobutenes

Triads of isomeric N-alkyl-N-methyl-3-phenylthiophen-2-amines, N-methyl-3-alkyl-4-methylidene-3-phenylthietan-2-imines, and N-methyl-4-alkylsulfanyl-2-phenylcyclobut-2-en-1-imines (Alk = Me, Et, Bu) were synthesized from 1,3-dilithio-3-phenylpropyne, methyl isothiocyanate, and alkyl halides, and their fragmentation under electron impact was studied. Primary decomposition of the molecular ions of 2-aminothiophenes is determined by the localization of a radical cation center on the nitrogen atom, and it follows a path typical of alkyl(aryl)amines with elimination of hydrogen atom or methyl or propyl radical from the α-carbon atom in the N-alkyl substituent. Fragmentation of the iminothietanes involves cleavage of the four-membered ring in half to give neutral MeNCS molecule and 1-alkyl-1-phenylallene radical cation. Alkylsulfanyl(imino)-cyclobutenes undergo cleavage at the sulfur-containing side chain according to general relations holding in the fragmentation of alkyl sulfides.     

Acetylene-allene rearrangement of propargyl systems X—CH2—C≡CH (X = H,Me, NMe2, OMe,F, SMe): an ab initio study

Acetylene—allene rearrangement in propargyl systems XCH₂CHCH (X = H, Me, NMe₂, OMe, F, and SMe) was studied using the ab initio approach. The relative stabilities of the starting and final propyne structures and the corresponding allenes as well as the structure of intermediate carbanions were considered. n--Conjugation was shown to dominate in allene stabilization while the inductive effect of heteroatomic substituents makes at least comparable contribution to stabilization (or destabilization) of the propynyl structure. In particular, relative instability of 1-methoxypropyne can be rationalized by high electronegativity of O atom, which leads to dramatic decrease in the total electron density in the region of the neighboring CC triple bond. The influence of substituents on the mobility of the migrating proton was considered for the gas phase and with solvation effects included. Calculations involving electron correlation at the MP2 level of theory were shown to be insufficient for correct reproduction of the energy differences between the corresponding propynes and allene structures. The results of MP4 calculations with inclusion of ZPE correction are in good agreement with the available experimental data.     

Structure of gaseous ω-acyloxyalkyltrihalosilanes

Conclusions A detailed analysis of the pathways for the mass spectrometric decomposition of -acyloxyalkyltrihalosilanes indicates the absence of an intramolecular coordination interaction of the silicon and carbonyl oxygen in the gas phase.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2596–2598, November, 1986.     

(Aroyloxymethyl)trifluorosilanes: a new class of pentacoordinate silicon compounds

A new class of organosilicon compounds containing a pentacoordinate silicon atom, (aroyloxymethyl)trifluorosilanes (AFS), has been prepared. The presence of an intramolecular coordinate F₃Si ← OC bond is supported by X-ray diffraction, IR spectroscopy and dipole moment data. Si ← O coordination in AFS has been shown to remain intact in the gaseous and liquid states below 420 K as well as in solution in most organic solvents. The dielectric constant of the medium significantly affects the nature of the coordinate Si ← O bond and that of the SiF, CO, COC bonds. In pyridine the intramolecular coordinate Si ← O interaction is disturbed or greatly weakened.At 420–500 K a reversible reaction takes place: ArC$\text{OOCH}{}_2\text{Si}$F₃ α ArCOOCH₂SiF₃ The changes in enthalpy and entropy are equal in this case: ?△H  8.1 ± 0.7 kcal/mol; ?°_S  15.3 ± 0.8 e.u. _T  450 K An assignment of bands in the IR spectra of AFS resulting from vibrations of atoms in the SiF₃, >CO and COC groups is given. The electron impact-induced primary disintegration of the molecular ion 4-XC₆H₄COOCH₂Si

mainly involves abstraction of a fluorine atom.     

Organylthiochloroacetylenes: V. Dimerization of Alkylthiochloroacetylenes in the Presence of Sodium Sulfite

Alkylthiochloroacetylenes dimerize at room temperature in the system sodium sulfite-polar nonhydroxyl solvent (DMSO, DMF, HMPA) to form in 40-63% yields (Z)-1,4-bis(alkylthio)-1,2-dichloro-1- buten-3-ynes which are promising polyfunctional monomers and building blocks for fine organic synthesis. The structure of the resulting dimers was established by means of IR and ¹H and ¹³C NMR spectroscopy, X-ray fluorescent analysis, and dielcometry and confirmed by mass spectrometry and elemental analysis.     

Cyclosilethynes containing exocyclic cyclopentyl and cyclohexyl groups

The reaction of BrMgCCSiMe₂CCSiMe₂CCSiMe₂CCSiMe₂CCMgBr with chloro(cyclopentyl)(methyl)silane in a large excess of THF gave 1-cyclopentyl-1,4,4,7,7,10,10,13,13-nonamethyl-1,4,7,10, 13-pentasilacyclopentadeca-2,5,8,11,14-pentayne. Similarly, 1,10-di(cyclopentyl)- or 1,6-di(cyclopentylmethyl)-1,4,4,7,7,10,13,13,16,16-decamethyl-1,4,7,10,13,16-hexasilacyclooctadeca-2,5,8,11,14,17-hexaynes were synthesized from BrMgCCSiMe₂CCSiMe₂CCMgBr and dichloro(cyclopentyl)methylsilane or dichloro(cyclopentylmethyl)(methyl)silane. Condensation of Me₂Si(CCMgBr)₂ with dichloro(cyclohexyl)-methylsilane afforded 1,7-di(cyclohexyl)-1,4,4,7,10,10-hexamethyl-1,4,7,10-tetrasilacyclododeca-2,5,8,11-tetrayne.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 8, 2004, pp. 1282–1284.Original Russian Text Copyright © 2004 by O. Yarosh, Zhilitskaya, N. Yarosh, Albanov, Klyba, Voronkov.This revised version was published online in April 2005 with a corrected cover date.     

Mass spectra of 3,6-dihalo-4,4-dimethyl-1,4-selenasilafulvenes and 2,4-dihalo-2-dihalomethyl-3,3-dimethyl-1-selena-3-silacyclopent-4-enes

The behavior of new heterocyclic systems, viz., 3,6-dihalo-4,4-dimethyl-1,4-selena- silafulvenes 1a, b and 2,4-dihalo-2-dihalomethyl-3,3-dimethyl-1-selena-3-silacyclopent-4-enes 2a, b (Hal =Cl, Br), was studied under conditions of electron ionization and thermal decomposition. Their fragmentation is accompanied by skeletal rearrangements, and the positive charge is localized mainly on ions containing silicon. Selenasilafulvenes 1a, b form stable molecular ions. Selenasilacyclopent-4-ene 2a decomposes partially and compound 2b decomposes completely in the gas phase with the elimination of a hydrogen halide and a halogen molecules.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 639–642, March, 2005.The term “contribution” implies the ratio of the sum of peak intensities of all isotope varieties of the ion under consideration to the total ion current.     

Thermal transformations of allyl 2-thienyl sulfide and selenide

In the gas phase at 350–410C allyl 2-thienyl sulfide is converted to thiophene-2-thiol, di(2-thienyl) sulfide, and 2-methylthieno[2,3-b]thiophene. In the presence of acetylene thieno[2,3-b]thiophene is formed in addition to these products. Allyl 2-thienyl selenide is converted quantitatively to 2,3-dihydro-2-methylselenopheno[2,3-b]thiophene during fractional distillation in vacuo. Thiophene, di(2-thienyl) selenide, di(2-thienyl) diselenide, thiophene-2-selenol, and 2-methylselenopheno[2,3-b]thiophene are formed in addition to these compounds in the thermolysis of allyl thienyl selenide in the gas phase. In the presence of acetylene the thermal decomposition of allyl thienyl selenide is accompanied by the formation of selenophene.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1312–1316, October, 1991.