Sulfonated polyether (ether) ketone or sulfonated PEEK (sPEEK) membranes are one possible candidate for proton-transfer membranes in hydrogen fuel cells. Reaction with hydroxy radicals is expected to be a significant source of degradation of these membranes during fuel cell operation. In this work, the reactivity of the sPEEK polymer molecule with OH radicals is studied by M062X hybrid density functional calculations of the energetics of several reaction paths in a water environment as modeled by polarized continuum model calculations. Reactants, products, encounter minima and transition states are optimized for a reaction pathway in which OH addition is followed by acid-catalyzed water elimination which cationizes the polymer, degradation is expected to follow this reaction as the unstable cation then undergoes bond-breaking or other reactions. Two pathways for this acid-catalyzed cationization, one in which a water molecule plays the role of an additional co-catalyst, are reported. Further calculations explore reaction pathways in which addition of OH to the polymer is followed by bond breaking reactions which would break the polymer chain or the bond between the polymer and sulfonyl groups. Examination of the free energy barriers to all these reactions, relative to reactants, suggests that these direct bond-breaking reactions may compete somewhat with acid-catalyzed water elimination following OH addition.

Polymer electrolyte membrane fuel cells are expected to continue to play a role in the development of alternative energy sources. Sulfonated polyether (ether) ketone, or sulfonated PEEK (sPEEK), membranes are one possible candidate for fuel cell membranes. In this work, the reactivity of the sPEEK polymer molecule with H radicals is studied by M062X hybrid density functional calculations. The energetics of relevant reaction paths were computed in both gas phase and a water environment as modeled by polarized continuum model calculations. Results suggest a simple degradation process in which the addition of H radicals to aromatic rings within the polymer is followed by bond-breaking processes within the polymer chain.

Continuing advances in computational chemistry has permitted quantum mechanical calculation to assist in research in green chemistry and to contribute to the greening of chemical practice. Presented here are recent examples illustrating the contribution of computational quantum chemistry to green chemistry, including the possibility of using computation as a green alternative to experiments, but also illustrating contributions to greener catalysis and the search for greener solvents. Examples of applications of computation to ambitious projects for green synthetic chemistry using carbon dioxide are also presented.

The structures and IR spectra of CF3OCH3, CF3OCF2H, and CF3OCF2CF2H and corresponding alkanes CF3CH3, CF3CF2H, and CF3CF2CF2H have been calculated using the B3LYP method with a 6-311G(2d,2p) basis set. The calculated IR spectra are consistent with, and provide additional confidence in, the available experimental data.

The structures and IR spectra of CF 3 OCH 3 , CF 3 OCF 2 H, and CF 3 OCF 2 CF 2 H and corresponding alkanes CF 3 CH 3 , CF 3 CF 2 H, and CF 3 CF 2 CF 2 H have been calculated using the B3LYP method with a 6-311G(2d,2p) basis set.The calculated IR spectra are consistent with, and provide additional confidence in, the available experimental data.

Ab initio density functional and molecular orbital calculations provide singlet and triplet electronic potential energy surfaces for the reactions of CF3CH2I+O(3P) leading to OI and HF eliminations, reactions which have been the subject of recent experimental studies. A barrier to OI formation occurs on the triplet potential energy surface; there is no reverse barrier to OI formation on the singlet pathway. Findings suggest that two competing pathways may form HF. One is an addition-insertion-elimination process involving insertion of O into the C-I bond. The alternate path involves OI elimination, addition of an O atom to CF3CH2, and subsequent HF elimination. The computed reactant pathways and energetics are discussed in relation to recent experiments.

The ESR spectrum of the chain-end radical RCF2CF2* detected in Nafion perfluorinated membranes exposed to the photo-Fenton reagent was accurately simulated by an automatic fitting procedure, using as input the hyperfine coupling tensors of the two F alpha and two F beta nuclei as well as the corresponding directions of the principal values from density functional theory (DFT) calculations. An accurate fit was obtained only for different orientations of the hyperfine coupling tensors for the two F alpha nuclei, indicating a nonplanar structure about the C alpha radical center. The fitted isotropic hyperfine splittings for the two F beta nuclei in the Nafion radical, 24.9 and 27.5 G, are significantly larger than those for the chain-end radical in Teflon (15 G), implying different radical conformations in the two systems. The excellent fit indicated that the geometry and electronic structure of free radicals can be obtained not only from single-crystal ESR spectroscopy, but also, in certain cases, from powder spectra, by combination with data from DFT calculations. The optimized structures obtained by DFT calculations for the CF3CF2CF2CF2* or CF3OCF2CF2* radicals as models provided additional support for the pyramidal structure determined from the spectral fit. Comparison and analysis of calculated and fitted values for the hyperfine splittings of the two F beta nuclei suggested that the radical detected by ESR in Nafion is ROCF2CF2*, which originates from attack of oxygen radicals on the Nafion side chain. The combination of spectrum fitting and DFT is considered important in terms of understanding the hyperfine splittings from 19F nuclei and the different conformations of fluorinated chain-end-type radicals RCF2CF2* in different systems, and also for elucidating the mechanism of Nafion fragmentation when exposed to oxygen radicals in fuel cell conditions.

Smog chamber/FTIR techniques were used to measure (Cl + n-CxF2x+1CHO, x = 1, 3, 4) = (2.1 +/- 0.5) x 10(-12) and k(OH + n-CxF2x+1CHO, x = 1, 3, 4) = (6.5 +/- 1.2) x 10(-13) cm(3) molecule(-1) s(-1) in 700 Torr of N-2, or air, at 296 +/- 2 K. Cl-initiated oxidation of n-CxF2x+1CHO in the presence of NO in air diluent gave COF2 in molar yields of 91 +/- 11%, x = 1; 273 +/- 36%, x = 3; and 371 +/- 44%, x = 4. Small quantities (molar yields less than or equal to 3%) of CF3ONO2 and n-CxF2x+1C(O)O2NO2 were also observed. IR spectra of n-CxF(2x+1)C(O)O2NO2 (x = 1, 3, 4) are reported. Results are discussed with respect to the atmospheric degradation of fluorinated aldehydes, CxF2x+1CHO.

Ferricyanide oxidation of 1,4,5,6-tetrahydro-2,4-dimethyl-6-(2'-pyridyl)-1,2,4,5-tetrazin-3(2H)-one (pvdH3) produces the stable chelating free radical 1,5-dimethyl-3-(2'-pyridyl)-6-oxoverdazyl (pvd) as an orange solid. Combination of group 12 metal halides with the ligand pvdH3 in acetonitrile results in precipitation of metal complexes. The mercuric chloride complex crystallizes in the monoclinic space group P2(1/c) with unit cell dimensions a = 8.5768(8) A, b = 19.1718(17) A, c = 8.5956(8) A, beta = 90.405 degrees, and V = 1413.4(2) A3. The mercuric ion is tricoordinate with a distorted trigonal planar geometry. Cadmium iodide and zinc chloride induce ring opening of the tetrazine resulting in pentacoordinate complexes of a hydrazone ligand. The cadmium iodide complex crystallizes in the triclinic space group P1 with cell dimensions a = 7.7184(8) A, b = 8.0240(9) A, c = 13.348(2) A, alpha = 97.876(4) degrees, beta = 95.594(6) degrees, gamma = 107.304(6) degrees, and V = 773.40(21) A3. Oxidation of all three metal complexes produces verdazyl radicals. Metal coordination is indicated by small changes in the EPR spectrum and by changes in the UV-visible spectrum, in particular the changes in the position of bands in the visible region. The metal halide-pvd complexes can also be synthesized by direct combination of metal halides with the free radical.

A room-temperature molten salt has been prepared from AuCl3 and l-ethyl-3-methylimidazolium chloride (EMIC). At a ratio of 1 mol of AuCl3 to 2 mol of EMIC, the salt is a bright yellow-orange and shows Raman spectral features at 170, 328, and 352 cm(-1) indicating the presence of AuCl4-. Ab initio calculations indicate that a dinuclear Au2Cl7- species containing a bridging chlorine should be stable, but no such species has been observed.