Electron attachment to SF5X compounds: SF5C6H5, SF5C2H3, S2F10, and SF5Br, 300-550 K

Rate constants and ion product channels have been measured for electron attachment to four SF5 compounds, SF5C6H5, SF5C2H3, S2F10, and SF5Br, and these data are compared to earlier results for SF6, SF5Cl, and SF5CF3. The present rate constants range over a factor of 600 in magnitude. Rate constants measured in this work at 300 K are 9.9+/-3.0x10(-8) (SF5C6H5), 7.3+/-1.8x10(-9) (SF5C2H3), 6.5+/-2.5x10(-10) (S2F10), and 3.8+/-2.0x10(-10) (SF5Br), all in cm3 s-1 units. SF5- was the sole ionic product observed for 300-550 K, though in the case of S2F10 it cannot be ascertained whether the minor SF4- and SF6- products observed in the mass spectra are due to attachment to S2F10 or to impurities. G3(MP2) electronic structure calculations (G2 for SF5Br) have been carried out for the neutrals and anions of these species, primarily to determine electron affinities and the energetics of possible attachment reaction channels. Electron affinities were calculated to be 0.88 (SF5C6H5), 0.70 (SF5C2H3), 2.95 (S2F10), and 2.73 eV (SF5Br). An anticorrelation is found for the Arrhenius A-factor with exothermicity for SF5- production for the seven molecules listed above. The Arrhenius activation energy was found to be anticorrelated with the bond strength of the parent ion.     

Rate Constant for the Ring Opening of the 2,2-Difluorocyclopropylcarbinyl Radical

The rate constant for the unimolecular ring opening of the 2,2-difluorocyclopropylcarbinyl radical was determined via its competitive bimolecular trapping by TEMPO. The value of this rate constant (3.4 x 10(11) s(-)(1) at 99.3 degrees C) is about 500 times larger than that of the parent, unfluorinated radical and about 5 times smaller than that of the trans-2-phenylcyclopropylcarbinyl radical.     

Atropisomerism of a monosubstituted perfluoro[2.2]paracyclophane. A combined synthetic, kinetic, spectroscopic and computational study

The product of S(N)Ar addition of the enolate of ethyl acetoacetate to perfluoro[2.2]para-cyclophane exists entirely as its enol tautomer 5. This enol exhibits two NMR signals for its enolic proton, and these signals were shown to derive from the presence of two, equal energy conformations that were observable as distinct, stable conformations at room temperature, but which when heated, interconverted with an energy barrier of 23.5 kcal mol(-1). These atropisomers were characterized by NMR, with details of this analysis being provided. Computational work corroborated the NMR conclusions, and provided additional insight into all structural, thermodynamic and kinetic results. Enol product 5 was cyclized, under basic conditions, to form a benzofuran product 6. Its structure was confirmed by NMR, with further structural and mechanistic insights being provided by calculations.     

Molecular structures and compositions of trans-1,2-dichlorocyclohexane and trans-1,2-difluorocyclohexane in the gas phase: an electron-diffraction investigation

The structures and compositions of gaseous trans-1,2-dichloro- (DCCH) and trans-1,2-difluorocyclohexane (DFCH), each of which may exist with the halogen atoms in a diaxial (aa) or diequatorial (ee) conformation, have been investigated by electron diffraction. The analysis was aided by rotational constants from microwave spectroscopy for the ee form of DFCH and by ab initio and density functional theory molecular orbital calculations for all species. The skeletons of the molecules have similar parameter values, but for the Cl-C-C-Cl and F-C-C-F fragments there are significant differences between the corresponding C-C-X bond angles and the X-C-C-X torsion angles in the two systems. There are also significant differences between the values of these parameters in the aa and ee forms of the same system. The composition of DCCH at 100 degrees C was measured to be 60(4)% aa, and that of DFCH at 70 degrees C was 42(7)% aa; the uncertainties are estimated 2sigma. From the preferred B3LYP/aug-cc-pVTZ calculations, the predicted theoretical composition is 51.2% aa for DCCH and 40.8% aa for DFCH. (Calculations at the levels B3LYP/6-31G(d) and MP2/6-31G(d) give similar results for DCCH, but both predict more aa than ee for DFCH.) Values (r(g)/A and angle(alpha)/degree) for some of the more important parameters of the aa/ee forms of DCCH are = 1.525(4)/1.525(6), C-Cl = 1.806(2)/1.787(2), angleC2-C1-Cl = 107.3(3)/111.5(3), angleC1-C2-C3 = 113.9(5)/111.6(5), angleC2-C3-C4 = 111.3(12)/109.9(12), and Cl-C2-C3-Cl = 165.3(9)/-59.4(9); and for DFCH C-C = 1.525(6)/1.520(9), C-F = 1.398(2)/1.390(2), angleC2-C1-F = 106.5(6)/109.2(6), angleC1-C2-C3 = 111.4(9)/110.9(9), angleC2-C3-C4 = 113.1(10)/113.1(10), and F-C2-C3-F = 171.1(37)/-67.2(37). The structures and compositions are discussed.     

Dimerizations of methylenecyclopropanes

The thermal [2+2] dimerization of methylenecyclopropanes, including methylenecyclopropane itself, is discussed. The effects of structural features on the ability of this reaction to occur are discussed in terms of the probable mechanism.     

Novel fluoropolymers formed by an unprecedented SRN1 condensation polymerization mechanism

A condensation copolymerization reaction between bis-phenol A and p-bis-(chlorodifluoro-methyl)benzene has been carried out to form a novel fluoropolymer that has excellent thermal and solubility properties. It is proposed that this polymerization reaction occurs via an unprecedented S_RN1 mechanism. This demonstration of the use of S_RN1 chemistry for condensation polymerizations of fluorinated monomers creates the opportunity for preparation of new fluoropolymers which are otherwise inaccessible.     

Bimolecular kinetic studies with high-temperature gas-phase 19F NMR: cycloaddition reactions of fluoroolefins

A gas-phase NMR kinetic technique has been used for the first time to obtain accurate measurements of rate constants of some bimolecular, second-order cycloaddition reactions. As a test of the potential use of this technique for the study of second-order reactions, the rate constants and the activation parameters for the cyclodimerization reactions of chlorotrifluoroethylene (CTFE) and tetrafluoroethylene (TFE) were determined in the temperature range 240-340 degrees C, using a commercial high-temperature NMR probe. Obtaining excellent agreement of the results with published data, the technique was then applied to the reaction of 1,1-difluoroallene with 1,3-butadiene, the results of which indicate that the use of gas-phase NMR for reaction kinetics is particularly valuable when a reagent is available only in small amounts and in cases where there are several competing processes occurring simultaneously. The major processes observed in this reaction are regioselective [2+2] and [2+4] cycloadditions, whose rates and activation parameters were determined [k2 = 9.3 x 10(6) exp(-20.1 kcal x mol(-1)/RT) L/mol(-1) x s(-1) and k3 = 1.2 x 10(6) exp(-18.4 kcal x mol(-1)/RT) L/mol(-1) x s(-)(1), respectively] in the temperature range 130-210 degrees C.     

New and convenient method for incorporation of pentafluorosulfanyl (SF5) substituents into aliphatic organic compounds

[reaction: see text] Use of Et3B as a catalytic initiator allows the convenient, regiospecific, and highly stereoselective addition of SF5Cl in high yield to a variety of alkenes and alkynes.