Structures and isomerizations of carbenoids H2CCCLiX (X  F,Cl)

Novel structures of H₂C?C?CLiX (X ? F, Cl) were determined using HF/STO-3G gradient method. Both of the carbenoids have two equilibrium structures, askew and linear forms, at the level of calculation. In the case X?F, the former is more stable, but in the case X=Cl, the latter is more stable. The frontier MOs are given and analyzed.     

Organocatalysis of CN/CN and CC/CN Exchange in Dynamic Covalent Chemistry

The reversibly formed C?N bond plays a very important role in dynamic covalent chemistry and the C?N/C?N exchange of components between different imine constituents to create dynamic covalent libraries has been extensively used. To facilitate diversity generation, we have investigated an organocatalyzed approach, using L ‐proline as catalyst, to accelerate the formation of dynamic libraries of [n×n] imine components. The organocatalysis methodology has also been extended, under somewhat modified conditions, to reversible C?C/C?N exchange processes between Knoevenagel derivatives of barbituric acid and imines, allowing for the generation of increased diversity.     

Random and sequential radical cotelomerizations of 3,3,3‐trifluoropropene (H2CCHCF3) with vinylidene fluoride (F2CCH2)

The synthesis of original cotelomers based on 3,3,3‐trifluoropropene (TFP) and vinylidene fluoride (VDF) with a general formula: R_F‐[CH₂? CF₂]_n? [CH₂? CH(CF₃)]_m? I (where n = 1–63, m = 2–640, and R_F = (CF₃)₂CF) was achieved by sequential and random cotelomerizations in the presence of R_FI. The radical cotelomerizations were initiated by thermal decomposition of different peroxide and persulfate initiators either in bulk, in solution (in the presence of acetonitrile or 1,1,1,3,3‐pentafluorobutane as the solvents), and in aqueous process (emulsion). Different adducts were obtained in good yield (50–70 wt %) with a relative proportion of each adduct depending on (i) the R₀ = [R_FI]₀/([TFP]₀+[VDF]₀) initial molar ratio, (ii) the reaction temperature, and (iii) C₀ = [In]₀/([TFP]₀+[VDF]₀). Random cotelomerization gave higher yields than those obtained from the sequential cotelomerization. When the concentration of the chain transfer agent increased, the molecular weights of the resulting poly(VDF‐co‐TFP) cotelomers decreased and showed that the R₀ ratio targeted the molecular weights (～700–66,000 g mol^?1). Some of the obtained molecular weights were exceptionally high for a (co)telomerization. The kinetics of the radical cotelomerization of VDF and TFP led to the determination of the reactivity ratios of both comonomers (r_VDF = 0.28 ± 0.07 and r_TFP = 2.35 ± 0.26 at 75 °C). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3964–3981, 2009     

Organocatalyzed and Uncatalyzed CC/CC and CC/CN Exchange Processes between Knoevenagel and Imine Compounds in Dynamic Covalent Chemistry

Molecular diversity generation through reversible component exchange has acquired great importance in the last decade with the development of dynamic covalent chemistry. We explore here the recombination of components linked by C?C and C?N bonds through reversible double‐bond formation, and cleavage in C?C/C?C and C?C/C?N exchange processes. The reversibility of the Knoevenagel reaction has been explored, and C?C/C?C C/C exchanges have been achieved among different benzylidenes, under organocatalysis by secondary amines such as L ‐proline. The substituents of these benzylidenes were shown to play a very important role in the kinetics of the exchange reactions. L ‐Proline is also used to catalyze the reversible C?C/C?C exchange between Knoevenagel derivatives of barbituric acid and malononitrile. Finally, the interconversion between Knoevenagel derivatives of dimethylbarbituric acid and imines (C?C/C?N exchange) has been studied and was found to occur rapidly in the absence of catalyst. The results of this study pave the way for the extension of dynamic combinatorial chemistry based on C?C/C?C and C?C/C?N exchange systems.     

Electron impact ionization of unstable enols: H2CCHOH,H2CC(OH)?CH3 and H2CC(OH)?C2H5

Ethenol, 2-hydroxypropene and 2-hydroxybutene-1 were prepared by low-pressure pyrolysis of cyclobutanol, 1-methylcyclobutanol and 1-ethylcyclobutanol, respectively. Mass spectra, ionization energies, appearance energies of metastable ions and kinetic energy releases were determined on a reverse Nier-Johnson double-focusing mass spectrometer. Mercury and CH₃ radicals from the pyrolysis of dimethylmercury were employed for calibration of the energy scale. The ionization energy of 2-hydroxybutene-1 is 8.55 ± 0.1 eV and the appearance energies of [C₂H₅CO]⁺ and [CH₃CO]⁺ from that molecule are 10.25 ± 0.1 and 10.40 ± 0.1 eV, respectively. Changes observed in metastable peak shapes for certain fragmentation reactions upon pyrolysis are discussed.