C3 epimerization and selective C2C3 bond fission of alkyl chrysanthemate

Treatment of alkyl chrysanthemate with Lewis acid leads to C₃ epimerization, while protonic acid treatment gives rise to selective C₂C₃ bond cleavage. The latter method is successfully applied to the synthesis of optically active tetrahydrolavandulol.     

Regioselective, nucleophilic carbon-carbon bond formation at the C4-position of indoles initiated by the aromatic Pummerer-type reaction

The treatment of the 5-(phenylsulfinyl)indoles with trifluoroacetic anhydride in the presence of carbon nucleophiles achieved the title reactions with complete regioselectivity.     

A theoretical study of the reaction of SiH2 with C2H2 and C2D2

Potential energy surfaces of the reaction of SiH₂ and C₂H₂ (and C₂D₂) have been calculated by means of ab initio molecular orbital theory at the QCISD/6-311G++(2df, 2p)//MP2/6-31G(d, p) level with corrections for the triple excitations to the QCISD energies. The barrier heights for the two reaction channels of the adduct, thus calculated, were further utilized for the dynamical calculation of the rate constants in the framework of quantum statistical Rice-Ramsperger-Kassel theory. Contributions of the rate constants of the various pathways to the total rate constant (K_T) for the disappearance of the reactants are critically examined and compared with experiment. The pressure dependence of K_T(C₂H₂) is primarily due to the formation of silirene. K_T(C₂D₂) is consistently higher than K_T(C₂H₂). The standard heat of formation of silirene is predicted to be 72.1 ± 3 kcal/mol. Rearrangement of silirene to vinylsilylene requires an activation energy smaller than that to silylacetylene.     

Regioselective addition of C-electrophiles and C-nucleophiles to a double bond of vinylacetylene—an example of a two-stage AdE reaction with formation of two new carbon-carbon bonds

Conclusions The two-stage reaction of electrophilic addition to a double bond of a C-electrophile and C-nucleophile, whose nature can be independently varied, was carried out for the first time on a dicobalthexacarbonyl complex of vinylacetylene used as an example. The reaction resulted in the formation of two carbon-carbon bonds. This opens up new possibilities for synthesizing polyfunctional compounds from vinylacetylene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2277–2284, October, 1985.     

Reactions of 12C+ with hydrocarbons at 296 K:carbon-carbon bond formation

Rate constants and product distributions have been determined for the ion-molecule reactions between ¹²C⁺ and methane, ethane, propane, ethylene, propylene, allene, acetylene, propyne and benzene. The measurements were carried out with the SIFT technique at a temperature of 296 ± 2K. The results provide insight into the build-up of carbon skeletons to form C⁺_n+1 ions and other competing modes of reaction at room temperature.     

The geometry, vibrational frequencies, thermochemistry, quadrupole moments and electronic structure of C2Na2: Comparison with C2Li2, C2H2, C2F2 and C2Cl2

The electronic structure of Na₂C₂ is studied using ab initio electronic structure methods and is compared to the companion molecule Li₂C₂. Both the linear D_∞h and planar structures are minima on the ground state potential surface with the planar D_2h conformation being the lowest energy form, similar to Li₂C₂. At the CCSD(t) level the planar form is more stable that the linear by 11.2 kcal/mol as compared with 7.34 kcal/mol for Li₂C₂. Both molecules are significantly ionic. The vibrational frequencies, atomization energy at 0 K, D₀, and the standard enthalpy of formation, are calculated and compared to those of Li₂C₂ as well as HCCH, FCCF and ClCCCl. We find D₀ and to be 331.1 and 84.92 kcal/mol for Li₂C₂ and 298.3 and 93.25 kcal/mol for Na₂C₂. We calibrate these by calculating the same quantities for HCCH, FCCF and ClCCCl.     

Kinetic isotope effects in the reaction H + C2H4 → C2H5

The high-pressure limiting rate constants of the reactions between H or D atoms and three isotopic ethylenes have been measured in the temperature range 206–461 K. Practically no isotope effects due to the differences between the ethylenes could be observed. This result does not agree with the prediction recently made by the activated complex theory.     

Condensation reaction of C4H4 with pyridine

C₄H₄⁺ reacts with pyridine (C₅H₅N) via the channels of proton transfer, charge transfer and condensation with H-elimination. The condensation reaction is of general interest in terms of basic chemistry and is the focus of the present study. By means of theoretical calculations and Fourier transform mass spectrometer experiments using deuterated pyridine and substituted pyridines, the structure of the product ion and the reaction pathways are investigated. From the experimental results we find that the H atom that is eliminated can originate from either pyridine or C₄H₄⁺. The experiments show that elimination of an H atom from C₄H₄⁺ is preferred and that there is an observable kinetic isotope effect. By replacing H atoms with methyl groups in ortho positions of pyridine, the experimental results also suggest possible steric blocking to the condensation. Based on the experimental observations and results of theoretical calculations of several possible structures of intermediates, transition states, and final product ions, a possible reaction scheme for the condensation-H-elimination is discussed.     

Reactions of C2(a 3πu) with CH4, C2H2, C2H4, C2H6, and O2 using multiphoton UV excimer laser photolysis

C₂(a ³π_u) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10^?6(x10^?10cm³s^?1) are reported for reactions with C₂H₄, C₂H₂, O₂, C₂H₆, and CH₄, respectively at 298 K. C₂(a ³π_u) fragments are generated by multiphoton ArF excimer laser photodissociation at C₂H₂, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C₂(a ³π_u) → (X ¹σ⁺_g) quenching channel. C₂ + C₂H₂ represents the one possible exception to the reactive channel.     

Formation of C1/C2-bromo-/chloro-hydrocarbons by haloperoxidase reactions

Summary We report here the first results of a study of the enzymatic formation of halogenated C₁/C₂-hydrocarbons from natural, biochemically relevant molecules using enzymes such as chloroperoxidase (CPO) or horseradish peroxidase (HRP). As halogen sources KBr, NaCl or a sea salt solution were utilized. The haloform reaction was used as a subsequent reaction to yield the halogenated methanes and ethanes from the halogenated substrate molecules. The products of the incubations were analyzed by HRGC/ECD. With these in vitro reactions we attempted to investigate possible biochemical pathways for the formation of some volatile halogenated organic compounds which are assumed to be of biogenic origin. Most of the incubations with KBr formed bromoform as the main product together with dibromo-chloro-methane and 1,1,2,2-tetrachloroethane as by-products. Incubations with NaCl result in chloroform as the main product in analogy to the formation of bromoform. The reaction with sea salt yields no major product but a spectrum of halogenated C₁/C₂-hydrocarbons. Incubations of a water extract of algae meal without any further source of Cl^–/Br^–-ions yield CHCl₃ as the main product and other mixed halogenated methanes as side products. Blank reactions were carried out without enzyme, H₂O₂ or substrate to show that the products of the incubations are formed enzymatically and to exclude the possibility of normal hypohalogenic reactions of the halide, H₂O₂ and the substrate.     

Vapour-liquid equilibrium data for the systems C2H6 + N2, C2H4 + N2, C3H8 + N2, and C3H6 + N2

High pressure vapour-liquid equilibrium data for the C₂H₆ + N₂, C₂H₄ + N₂, C₃H₈ + N₂, and C₃H₆ + N₂ systems are presented. The data are obtained isothermally in the range from 200 K to 290 K. For each point of data, temperature, pressure and liquid and vapour phase mole fractions are measured.Values for the vapour phase mole fractions are calculated from the obtained pressure, temperature and liquid phase mole fractions. The calculated values are compared with the experimental results, and it is found that the average mean deviation between calculated and experimental mole fractions is less than 0.009 for the systems considered in this work.     

Formation and structural study of a mixed ene/enyl ligand on reaction of [Ru(C5Me5)Cl2]2 with 1,3-cyclononadiene

The reaction of [Ru(C₅Me₅)Cl₂]₂ with an excess of 1,3-cyclononadiene in the presence of metallic zinc leads to Ru(C₅Me₅)(1,2,3,6,7-η⁵-C₉H₁₃), in which the nine-membered ring provides both allyl and olefin coordinations, linked together on each side by C₂H₄ bridges. The complex has been characterized analytically, spectroscopically, and structurally.     

Thermal gas-phase reaction of perfluorobuta-1,3-diene with NO2

The reaction of NO₂ with perfluorobuta-1,3-diene, CF₂CFCFCF₂ (C₄F₆), has been studied at 312.9, 323.0, 333.4, 396.0 and 418.0 K, using a conventional static system. The products formed in the temperature range 312.9-333.4 K were CF₂CFCF(NO₂)CF₂(NO₂) (I), CF₂(NO₂)CFCFCF₂(NO₂) (II), CF₂CFCF(NO₂)C(O)F (III) and CF₂(NO₂)CFCFC(O)F (IV) and FNO. The formation of these compounds was detected performing infrared and Raman spectra. The infrared spectrum shows a band at 1785 cm⁻¹, characteristic to the terminal -CFCF₂ group and the Raman spectrum shows a band located at 1733 cm⁻¹, corresponding to -CFCF- group. It indicates, that in this temperature range, NO₂ attacks initially only one double bound of CF₂CFCFCF₂. Since the intermediate radical CF₂CFCFCF₂(NO₂) formed in this process is allylic in nature, so there is no isomerization involved in this process, but rather the allylic radical is able to add the second NO₂ either to CF₂ or CFCF₂(NO₂) end, forming the corresponding products. At 396.0 and 418.0 K different products were observed: CF₂(NO₂)CF(NO₂)C(O)F (V), NO, CF₃C(O)F, C(O)F₂ and traces of epoxide of tetrafluoroethene, showing that, at these temperatures, both double bonds are attacked by NO₂ and detachment of CF₂ group is produced. The mechanisms consistent with experimental results in the temperature range 312.9-333.4 and at 396.0 and 418 K are proposed.     

Selective formation of C60F18(g) and C60F36(g) by reaction of [60]fullerene with molecular fluorine

Fluorination of C₆₀(s), C₆₀(s)-MnF₂(s), C₆₀(s)-NiF₂(s) and C₆₀(s)-MnF₃(s) mixtures has been studied by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination is selective when fullerene reacts with the fluorine chemisorbed on the MnF₂ surface. When the MnF₂ content in the initial mixture is at least 90 mol% both C₆₀F₁₈ and C₆₀F₃₆ are selectively formed. Under certain conditions, mixtures predominantly containing one of three compounds C₆₀F₃₈, C₆₀F₄₀, and C₆₀F₄₂ can be obtained. A consecutive change of the main fluorination products (C₆₀F₁₈ and C₆₀F₃₆) takes place at constant temperature (720 K) and on fluorine admission. A quantitative explanation of this fact is given. Selective fluorination of C₆₀(s) by molecular fluorine is compared with solid-phase fluorination using MnF₃(s) as a fluorinating agent.     

Stereospecific carbon-carbon bond formation by the reaction of a chiral episelenonium ion with aromatic compounds

The stereospecific exchange of a hydroxyl group of chiral alcohols bearing a pyridylseleno group on the adjacent carbon atom with aromatic compounds occurred smoothly in the presence of Lewis acid.     

Elucidation of biochemical formation of C1/C2-(bromo-/chloro)-hydrocarbons

Summary To elucidate possible biochemical pathways of the formation of halogenated C₁/C₂-hydrocarbons we investigated the product pattern of the reaction of chloroperoxidase (CPO) with natural substances including the haloform reaction as a second step. The analysis of the reaction products was performed by HRGC-ECD. We report here first results. As substrates we used acetic acid and acetone while KBr and NaCl served as halogen sources. The system acetic acid/KBr/CPO formed tribromomethane as the main product, with dibromochloromethane (CHBr₂Cl) and 1,1,2,2-tetrachloroethane as by-products. Incubation with acetone resulted in the formation of CHBr₃ as the main product, with CHBr₂Cl, CH₂Br-CH₂Br, CHCl₂-CHCl₂, CHCl₂-CCl₃ and trichloroethene as side products, while the reaction of acetone with NaCl and CPO yielded chloroform as a main product.Results partly presented at the ANAKON '91 in Baden-Baden, April 22–24, 1991     

Time-resolved C2 swan emission from short-pulse UV fragmentation of CO: evidence for two C2 formation mechanisms

We have studied C₂ Swan (d³Π → a³ Π_u) emission resulting from multiphoton UV excitation of CO. Population of d³Π proceeds through distinct early and late processes, the former giving rise only to normal Swan emission. The late process is responsible for v = 6 enhancement (high-pressure bands), and it dominates time-averaged emission in an bands for ? 10 Torr of CO.