Enthalpies of formation for 14 C2–C4 fluorinated hydrocarbons were calculated with nine popular ab initio and density functional theory methods: B3LYP, CBS-QB3, CBS-APNO, M06, M06-2X, ωB97X, G4, G4(MP2)-6X, and W1U via several series of isodesmic reactions. The recommended ideal gas phase ΔHf298° (kcal mol(–1)) values calculated in this study are the following: −65.4 for CH3CH2F; −70.2 for CH3CH2CH2F; −75.3 for CH3CHFCH3; −75.2 for CH3CH2CH2CH2F; −80.3 for CH3CHFCH2CH3; −108.1 for CH2F2; −120.9 for CH3CHF2; −125.8 for CH3CH2CHF2; −133.3 for CH3CF2CH3; −166.7 for CHF3; −180.5 for CH3CF3; −185.5 for CH3CH2CF3; −223.2 for CF4; and −85.8 for (CH3)3CF. Entropies (S298° in cal mol(–1) K(–1)) were estimated using B3LYP/6-31+G(d,p) computed frequencies and geometries. Rotational barriers were determined and hindered internal rotational contributions for S298°, and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation, with direct integration over energy levels of the intramolecular rotation potential energy curve. Thermochemical properties for the fluorinated carbon groups C/C/F/H2, C/C2/F/H, C/C/F2/H, C/C2/F2, and C/C/F3 were derived from the above target fluorocarbons. Previously published enthalpies and groups for 1,2-difluoroethane, 1,1,2-trifluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,1,2,2-pentafluoroethane, 2-fluoro-2-methylpropane that were previously determined via work reaction schemes are revised using updated reference species values. Standard deviations are compared for the calculation methods.

Emissions of gaseous mercury from combustion sources are the major source of Hg in the atmosphere and in environmental waters and soils. Reactions of Hg(o)(g) with halogens are of interest because they relate to mercury and ozone depletion events in the Antarctic and Arctic early spring ozone hole events, and the formation of Hg-halides (HgX2) is a method for removal of mercury from power generation systems. Thermochemistry and kinetics from published theoretical and experimental studies in the literature and from computational chemistry are utilized to compile a mechanism of the reactions considered as contributors to the formation of HgX2 (X = Cl, Br, I) to understand the reaction paths and mechanisms under atmospheric conditions. Elementary reaction mechanisms are assembled and evaluated using thermochemistry for all species and microscopic reversibility for all reactions. Temperature and pressure dependence is determined with quantum Rice Ramsperger Kassel (RRK) analysis for k(E) and master equation analysis for fall-off. We find that reactions of mercury with a small fraction of the reactor surface or initiation by low concentrations of halogen atoms is needed to explain the experimental conversion of Hg to HgX2 in the gas phase. The models do not replicate data from experiments that do not explicitly provide an atom source. The Hg insertion reaction into X2 (Hg + X2 → HgX2) that has been reported is further studied, and we find agreement with studies that report high barriers. The high barriers prevent this insertion path from explaining the experimental data on HgX2 formation and Hg conversion under atmospheric conditions. Mechanism studies with low initial concentrations of halogen radicals show significant conversion of Hg under the experimental conditions.

Applications of a variational coupled-electron pair approach to the calculation of intermolecular interaction in the framework of the VB theory: Study of the van der Waals complex He-CH 4Ar and CH4 van der Waals complexes of 1 and 2fluoronaphthalene: A perturbed spherical top attached to a surface Accurate spectroscopic constants for the Cd(1 S,3 P,1 P)-H2 van der Waals complexes: A theoretical study J. Chem. Phys. 100, 8251 (1994); 10.1063/1.466768Halfcollision studies: Action spectroscopy of electronic energy transfer within the CdCH4 van der Waals complex The CdctS,3,lp)-CH 4 interaction is studied for the C 3v vertex-on Cd(IS,3,lp)-HCH 3 and face-on Cd(IS,3,lp)-H 3 CH approaches as well as the C 2v cdcIS,3,lp)-H 2 CH 2 edge-on approach of the metal atom to methane using extensive ab initio multireference configuration interaction plus second order multireference M011er-Plesset calculations. The ground state CdcIS)-CH 4 is totally repulsive for the C 3v vertex-on and C 2v edge-on approaches. Only a stable face-on CdeS)-H 3 CH complex was found. Although vertex-on and edge-on minima were found for the Cdep)-CH 4 excited complexes, they are less attractive than the corresponding Cde P)-H3CH face-on exciplexes. The optimal orientation of the face-on occupied 5p orbital of Cd(5s5p) is that which minimizes the overlap with C-H bonds leading to a ,,3rry" exciplex. For the CdctP)-CH 4 interaction, two face-on and two edge-on very stable complexes (all with De> 1300 cm-I ) were found. The CdctS)-H 3 CH cIA I ) complex was found to have a 185 cm-l well at 8.03 a.u. Both excited P states present shorter equilibrium distances-the Cdep)-H 3 CH eEl exciplex has a 799 cm-l well at 6.08 a.u., while the CdctP)-H 3 CH exciplex eE) has a 1337 cm-l well at 5.57 a.u. These results are in good agreement with the recent experimental values X IO+ctS)-CDe= 121 cm-l , R e =7.9 a.u.); A 30+ep)-(De=677 cm-I, R e =5.80 a.u.); and Ip-(De~1300 cm-I, R e =5.59 a.u.) obtained by Wallace and Breckenridge [J. Chem. Phys. 97, 2318 (1992)]. The present work confirms the C 3v facial nature of the observed ctS) ground and ep) excited complexes. The present results are inconclusive as to the facial or edge-on nature of the ~dctP)-CH4 exciplex, but they preclude the C 3v vertex-on possibility.

We present an experimental and computational study of the reaction of aryl substituted benzyl 1-alkynyl sulfides with potassium alkoxide in acetonitrile, which produces 2-aryl 2,3-dihydrothiophenes in poor to good yields. The cyclization is most efficient with electron withdrawing groups on the aromatic ring. Evidence indicates there is rapid exchange of protons and tautomerism of the alkynyl unit prior to cyclization. Theoretical calculations were also conducted to help rationalize the base induced 5-endo cyclization of benzyl 1-propynyl sulfide (1a). The potential energy surface was calculated for the formation of 2,3-dihydrothiophene in a reaction of benzyl 1-propynyl sulfide (1a) with potassium methoxide. Geometries were optimized with CAM-B3LYP/6-311+G(d,p) in acetonitrile with the CPCM solvent model. It is significant that the benzyl propa-1,2-dien-1-yl sulfane (6) possessed a lower benzylic proton affinity than the benzyl prop-2-yn-1-yl sulfane (8) thus favoring the base induced reaction of the former. From benzyl(propa-1,2-dien-1-yl sulfane (6), 2,3-dihydrothiophene can be formed via a conjugate base that undergoes 5-endo-trig cyclization followed by a protonation step.