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Intermolecular interaction potentials for benzene, propane, perfluoromethane, furan, thiophene, selenophene, pyridine, phosphorine dimers and benzene-methane, benzene-chlorobenzene, benzene-bromobenzene complexes were calculated using the BLYP, B97 (B98), BP86, BPBE, PBE, PW91, B3LYP, B3PW91, BMK, PBE1PBE, APF, ωB97 (ωB97X), CAM-B3LYP, LC-ωPBE, B2PLYP, mPW2PLYP, TPSS, M06L, M05, M052X, M06, M062X and M06HF functionals with Grimme's dispersion correction methods of D2, D3 and D3BJ versions. The calculated potentials were compared with the CCSD(T) level potentials to evaluate the accuracy of the dispersion corrected DFT methods for calculating the intermolecular interaction energies of hydrocarbon molecules and molecules including heteroatoms (N, P, O, S, Se, F, Cl and Br). The performance of the calculations depends strongly on the choice of the functional and the dispersion correction method. None of the combinations of the functionals and the dispersion correction methods can reproduce well the CCSD(T) level interaction potentials of all the complexes. The improvement of the functionals from GGA to hybrid GGA, meta GGA or meta hybrid GGA is not essential for improving the performance. The significant functional dependence suggests that the scaling factors, which were determined for each functional by fitting, are the cause of the dependence. The performance of the calculations of hydrocarbon molecules is much better than that of the molecules including heteroatoms. A smaller number of molecules including heteroatoms were used for the reference data of the fitting compared with hydrocarbon molecules, which might be one of the causes of the worse performance of the calculations of molecules including heteroatoms.

Isocyanurates are cyclic trimers of isocyanate molecules. They are generally known as highly thermostable compounds. However, it is interesting how the thermal stabilities of the isocyanurate molecules will be altered depending on the substituents of their three nitrogen atoms. We performed computational investigations on the thermochemical behaviors of isocyanurate molecules with various alkyl and phenyl substituents. The cyclotrimerization processes of isocyanates are highly exothermic. Our best estimate of the enthalpy change for the cyclotrimerization of methyl isocyanate into trimethyl isocyanurate was −66.4 kcal mol−1. Additional negative cyclotrimerization enthalpy changes were observed for n-alkyl-substituted isocyanates. This trend was enhanced with an extension of n-alkyl chains. Conversely, low negative cyclotrimerization enthalpy changes were shown for secondary and tertiary alkyl-substituted isocyanates. The n-alkyl-substituted isocyanurates were shown to be stabilized due to attractive dispersion interactions between the substituents. Meanwhile, the branched alkyl-substituted isocyanurates were destabilized due to the deformation of their isocyanurate rings. For various alkyl-substituted isocyanates, the sum of the deformation energy of the isocyanurate ring and the intramolecular inter-substituent nonbonding interaction energies was found to be linearly correlated with their cyclotrimerization energies. The cyclotrimerization energy for phenyl isocyanate was shown to have significantly deviated from the linear relationship observed for the alkyl-substituted isocyanurates. This is probably attributable to a remarkable change in the orbital resonance interactions during the cyclotrimerization of phenyl isocyanate to triphenyl isocyanurate.

E–CF3CH=CHC2F5 is a promising substance that could be used as high temperature bump working fluid. In this study, the rate constants (k1) for the reaction of E−CF3CH=CHC2F5 with OH were measured by the relative rate method: k1 (298 K) = (9.10 ± 0.29) × 10−14 and k1 (253–328 K) = (7.56 ± 0.88) × 10−13 exp [−(632 ± 35)/T] cm3 molecule−1 s−1. The atmospheric lifetime of E−CF3CH=CHC2F5 was estimated to be 127 d, while its radiative efficiency (RE) was evaluated to be 0.198 W m−2 ppb−1. The estimated POCPs of E−CF3CH=CHC2F5 were estimated to be 0.5 and 0.2 for North-west European and USA urban conditions, respectively. The 20, 100, and 500-year time horizon global warming potentials (GWPs) of E−CF3CH=CHC2F5 were estimated to be 73, 20, and 6, respectively. CF3OOOCF3, CF3OOOC2F5, COF2, CO, and CO2 were identified as the carbon-containing products following the degradation of E–CF3CH=CHC2F5.

The rate constants for the gas-phase reactions of cyc-CF2CF2CF2CH=CH– with OH radicals were determined by a relative rate method between 253 and 328 K. The rate constant k1 at 298 K was measured to be (1.08 ± 0.04) × 10−13 cm3 molecule−1 s−1, and the Arrhenius expression was k1 = (3.72 ± 0.14) × 10−13 exp [(−370 ± 12)/T]. The atmospheric lifetime of cyc-CF2CF2CF2CH=CH– was calculated to be 107 d. The products and mechanism for the reaction of cyc-CF2CF2CF2CH=CH– with OH radicals were also investigated. CO, CO2, and COF2 were identified as the main carbon-containing products following the OH-initiated reaction. Moreover, the radiative efficiency (RE) was determined to be 0.143 W m−2 ppb−1, and the global warming potentials (GWPs) for 20, 100, and 500 yr were 54, 15, and 4, respectively. The photochemical ozone creation potential of the title compound was estimated to be 1.3.

The rate constants for the reactions of OH radical with (E)- and (Z)-isomers of CF3CF═CHCl and CHF2CF═CHCl have been measured over the temperature range of 250–430 K. Kinetic measurements have been performed using flash and laser photolysis methods combined with laser-induced fluorescence. Arrhenius rate constants have been determined as k((E)-CF3CF═CHCl) = (1.09 ± 0.03) × 10–12 · exp[(50 ± 10)K/T], k((Z)-CF3CF═CHCl) = (8.02 ± 0.19) × 10–13 · exp[−(100 ± 10)K/T], k((E)–CHF2CF═CHCl) = (1.50 ± 0.03) × 10–12 · exp[(160 ± 10)K/T], and k((Z)–CHF2CF═CHCl) = (1.36 ± 0.03) × 10–12 · exp[(360 ± 10)K/T] cm3 molecule–1 s–1. Infrared absorption spectra have also been measured at room temperature. The atmospheric lifetimes of (E)-CF3CF═CHCl, (Z)-CF3CF═CHCl, (E)-CHF2CF═CHCl, and (Z)-CHF2CF═CHCl have been estimated as 8.9, 20, 4.6, and 2.6 days, respectively, and their global warming potentials and ozone depletion potentials were determined as 0.23, 0.88, 0.060, and 0.016 and 0.00010, 0.00023, 0.000057, and 0.000030, re...

As a high-profile etching gas, perfluorocyclopentene (cyc-CF 2 CF 2 CF 2 CF=CF−) should be assessed for its atmospheric chemistry and environmental impact prior to expanding its industrial applications. However, the corresponding studies have been limited. In this study, the rate constants for the gas-phase reactions of cyc-CF 2 CF 2 CF 2 CF=CF− with OH radicals were determined by a relative rate method, and shown to be consistent with a theoretical computational results: k 1-exp. (298 K) = (4.43 ± 0.10) × 10 −14 , k 1-cal. (298 K) = 4.3 × 10 −14 , and k 1-exp. (253–328 K) = (3.39 ± 0.86) × 10 −13 exp(–(616 ± 78)/ T ) cm 3 molecule −1 s −1 . The atmospheric lifetime of cyc-CF 2 CF 2 CF 2 CF=CF− is 0.715 year, and its photochemical ozone creation potential is 0.48. Furthermore, the products and mechanism of the OH radical-initiated oxidation reactions were studied for the first time. The major products COF 2 , CO 2 , CO, and FC(O)OH are considered to have a negligible environmental effect. The radiative efficiency was determined as 0.246 W m −2 ppb −1 , and the global warming potentials (GWPs) with 20-, 100-, and 500- year time horizon were estimated as 188, 51, and 15, respectively. The GWP 100 value is significantly lower than those of the replacing targets (6630, 11100, 16 100, 23 500, and 9540 for CF 4 , C 2 F 6 , NF 3 , SF 6 , and c-C 4 F 8 , respectively).

The (E)- and (Z)-geometrical isomers of fluorinated propenes (CWZ = CY−CX3, W, X, Y, and Z = H or F) are computationally investigated. Our calculations show that geometrical isomers with two fluorine atoms located at the cis positions of the C C bond tend to undergo additional energy lowering compared to the trans isomers. Natural bond orbital analysis suggests that the origin of this lowering of energy is the same as that of the typical fluorine cis effects observed for 1,2-dihaloethenes. The barrier height magnitude of the internal rotation of the methyl or trifluoromethyl group is shown to be sensitive to the substitution patterns in the fluorinated propenes. The change in the rotational barrier heights is closely related to the differences in the magnitude of intramolecular repulsive non-bonded steric interactions. Furthermore, the π-bonds in fluorinated propenes are shown to be weaker for the derivatives possessing two fluorine atoms at both ends of the C C bond. The OH radical reactions of the fluorinated propenes are initiated by the attack of the OH radicals on the π-bond. Nevertheless, no obvious correlation is found between the rate constants for the OH radical reactions and the π-bond strengths of the fluorinated propenes.

The strengths of π-bonds in a series of fluorinated ethylenes have been computationally investigated, and the potential energy surfaces for thermal C C bond rotation in fluorinated ethylenes, as well as in ethylene, have been explored. The computed thermal rotational barrier values and the π-bond strengths obtained using Benson’s procedure show parallel trends. Our calculations indicate that the π-bond in CH2 = CHF is slightly stronger, and the one in CF2 = CF2 is noticeably weaker than that in CH2 = CH2. In addition, the stabilization effects of fluorine substitution have been evaluated for fluorinated ethylene molecules and for singlet biradical thermal rotation transition states. Considering these fluorine substituent effects, the change in the π-bond strength of a series of fluorinated ethylenes can be qualitatively interpreted.

Non-equilibrium behavior of liquid mixture of polyethylene glycol (PEG) and polypropylene glycol (PPG) is studied. During the phase variation of PEG/PPG mixture, time-resolved Fourier transform infrared (FTIR) spectra were collected by attenuated total reflection (ATR) technique to selectively capture the development and subsequent variation of PEG-rich phase, appearing within a layer of the sample adjacent to the measuring surface of the ATR diamond prism. The FTIR spectra were then subjected to a two-dimensional (2D) correlation method to elucidate subtle but important changes in the absorbance of spectral bands. 2D correlation spectra revealed fine details of the non-equilibrium system. During the phase variation, dissociation between PEG and PPG generates free PEG molecules first. The emergence of the free PEG molecules triggers the subsequent self-assembly via the development of intermolecular H-bonding between PEG molecules, which eventually generates bigger PEG aggregates.

Geometries of benzene complexes with C6F5X, C6H5X, and CF3X (X is I, Br, Cl, and F) were optimized, and their interaction energies were evaluated. The CCSD(T) interaction energies at the basis set limit (Eint) of C6F5X (X is I, Br, Cl, and F) with benzene were -3.24, -2.88, -2.31, and -0.92 kcal mol(-1). Eint of C6H5X (X is I, Br, and Cl) with benzene were -2.31, -1.97, and -1.48 kcal mol(-1). The fluorination of halobenzenes slightly enhances the attraction. Eint of CF3X (X is I, Br, Cl, and F) with benzene (-3.11, -2.74, -2.22, and -0.71 kcal mol(-1)) were very close to Eint of corresponding C6F5X with benzene. In contrast to the halogen bond of iodine and bromine with pyridine (n-type halogen bond acceptor) where the main cause of the attraction is the electrostatic interactions, that of halogen bond with benzene (p-type acceptor) is dispersion interaction. In the halogen bonds with p-type acceptors (halogen-π interactions), the electrostatic interactions and induction interactions are small. The overall orbital-orbital interactions are repulsive. The directionality of halogen bonds with p-type acceptors is very weak, owing to the weak electrostatic interactions, in contrast to the strong directionality of the halogen bonds with n-type acceptors and hydrogen bonds.

The stability of E/Z-alkoxyenamines from α-alkoxyaldehyde with pyrrolidine was discussed by conducting density functional theory (DFT) calculations with natural bond orbital (NBO) analysis.

The CCSD(T) level intermolecular interaction energies calculated for the CF4-CH4 complex are compared with those for the CF4-CF4 and CH4-CH4 complexes. The interactions in the CF4-CH4 complex is stronger than the average of the interactions in the CF4-CF4 and CH4-CH4 complexes. DFT-SAPT calculations show that the dispersion interactions in the CF4-CH4 complex, which are the primary source of the attraction, are nearly identical to the average of those in the CF4-CF4 and CH4-CH4 complexes, while the attractive electrostatic interactions in the CF4-CH4 complex is stronger than the average of those in the CF4-CF4 and CH4-CH4 complexes.

The rate constants for the reactions of OH radical with ( E)- and ( Z)-isomers of CF

Photooxidation of indene-C60 bisadduct (ICBA) and indene-C60 monoadduct (ICMA) was studied using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), IR spectroscopy, and density functional theory (DFT) calculations. MALDI-TOF MS suggested that the oxidation occurred on the fullerene cage of ICBA or ICMA and that the oxidation of ICBA proceeded faster than that of ICMA. The IR study and DFT calculation indicated that carbonyl substituents were generated upon photoirradiation. The effects of the oxidized ICMA were examined by measuring the device properties of organic photovoltaic (OPV) cells. The increase in energy levels of fullerene derivatives affects the stability against photooxidation negatively, while it increases the open circuit voltage of OPV devices. These results indicate that it is important to balance the OPV performance with stability against photooxidation.

Rate constants for the reactions of cyc-CF2CF2CF2CHFCH2 (k1) and trans-cyc-CF2CF2CF2CHFCHF (k2) with OH radicals were assessed by a relative rate method. The values were determined as (9.35 ± 5.83) × 10−13 exp[−(1197 ± 180)/T] and (8.02 ± 2.17) × 10−13 exp[−(1198 ± 80)/T] between 253 and 328 K; and (1.72 ± 0.05) × 10−14 and (1.43 ± 0.03) × 10−14 cm3 molecule−1 s−1 at 298 K, respectively. The atmospheric lifetimes were 2.8 and 3.2 years; the 100-year time horizon global warming potentials were estimated to be 211 and 241, respectively.

The diphenylprolinol silyl ether mediated asymmetric nitrocyclopropanation of α-substituted α,β-unsaturated aldehydes with bromonitromethane, followed by base-promoted isomerization was found to afford trans-nitrocyclopropanecarbaldehydes with all-carbon quaternary stereogenic centers with excellent diastereo- and enantioselectivities. DFT calculations indicated that the s-trans conformer of the iminium ion intermediate is more stable than the s-cis conformer. In addition, nucleophilic attack of the bromonitromethane anion to the iminium ion intermediate was calculated to occur preferentially from the opposite side of the bulky substituents of the pyrrolidine iminium intermediate.

Generation of 1 O 2 from poly-(3-hexylthiophene) (P3HT) irradiated in the presence of O 2 in chlorobenzene was investigated using ESR measurement, employing 2,2,6,6-tetramethylpiperidine (TEMP) as a spin trap. 1 O 2 was found to be formed with O 2 ˉ being produced in parallel at a branching ratio of 99:1. Additionally, the reaction of P3HT with 1 O 2 was investigated using an endoperoxide as the 1 O 2 source in CCl 4 by MALDI–TOF MS measurement. The upper limit of the rate constant for the reaction of P3HT with 1 O 2 was estimated using a kinetics simulation. These findings raise the understanding of the photo-oxidative degradation of P3HT.

The origin of the attraction in charge-transfer complexes (a p-hydroquinone-p-benzoquinone complex and benzene complexes with benzoquinone, tetracyanoethylene and Br2) was analyzed using distributed multipole analysis and symmetry-adapted perturbation theory. Both methods show that the dispersion interactions are the primary source of the attraction in these charge-transfer complexes followed by the electrostatic interactions. The natures of the intermolecular interactions in these complexes are close to the π/π interactions of neutral aromatic molecules. The electrostatic interactions play important roles in determining the magnitude of the attraction. The contribution of charge-transfer interactions to the attraction is not large compared with the dispersion interactions in these complexes.

The effect of silyl substituents in diphenylprolinol silyl ether catalysts was investigated. Mechanistically, reactions catalyzed by diphenylprolinol silyl ether can be categorized into three types: two that involve an iminium ion intermediate, such as for the Michael-type reaction (type A) and the cycloaddition reaction (type B), and one that proceeds via an enamine intermediate (type C). In the Michael-type reaction via iminium ions (type A), excellent enantioselectivity is realized when the catalyst with a bulky silyl moiety is employed, in which efficient shielding of a diastereotopic face of the iminium ion is directed by the bulky silyl moiety. In the cycloaddition reaction of iminium ions (type B) and reactions via enamines (type C), excellent enantioselectivity is obtained even when the silyl group is less bulky and, in this case, too much bulk reduces the reaction rate. In other cases, the yield increases when diphenylprolinol silyl ethers with bulky substituents are employed, presumably by suppressing side reactions between the nucleophilic catalyst and the reagent. The conformational behaviors of the iminium and enamine species have been determined by theoretical calculations. These data explain the effect of the bulkiness of the silyl substituent on the enantioselectivity and reactivity of the catalysts.

Rate constants for the gas-phase reactions of cyc-CF2CF2CF2CH2CH2– with the OH radicals were assessed by a relative rate method in the temperature range of 253–328 K, from which k1(T) = (8.52 ± 1.58) × 10−13 exp [(–1017 ± 53)/T] was derived for the Arrhenius equation. Its atmospheric lifetime was 1.6 years. The estimated photochemical ozone creation potentials (POCP) were 0.211 and 0.076 for North-west European and USA urban conditions, respectively. The radiative efficiency (RE) was measured as 0.200 W m−2 ppb−1, and the global warming potential (GWP) of the 100-year time horizon was estimated to be 107. The atmospheric oxidation mechanism of cyc-CF2CF2CF2CH2CH2– was studied by the experimental method. COF2, CO, and CO2 were identified as the main carbon-containing products. Additionally, the degradation mechanism of two analogous compounds, cyc-CF2CF2CF2CHFCH2– and cis-cyc-CF2CF2CF2CHFCHF–, were also investigated. COF2, HC(O)F, CO, and CO2 were observed as the main products.

Among 1,4-addition and 1,6-addition reactions, 1,4-addition reaction is the main reaction mode in the Michael reaction of α,β-γ,δ-diunsaturated aldehyde with several nucleophiles catalyzed by diphenylprolinol silyl ether via iminium ion intermediate. The 1,4-addition products, which possess excellent enantioselectivity and alkene moiety, are useful chiral building blocks. The ab initio calculation indicates that 1,4-addition reaction is preferable in terms of π-orbital coefficient and Mulliken/CHelpG atomic charge.

The rate constants of the reactions of n -C 4 F 9 OCH 3 ( k 1 ), i -C 4 F 9 OCH 3 ( k 2 ), n -C 4 F 9 OC(O)H ( k 3 ), and i -C 4 F 9 OC(O)H ( k 4 ) with OH radicals were studied in an 11.5-dm 3 environmental reaction chamber. k 1 and k 2 were determined to be (1.44 ± 0.33) × 10 –12 exp[–(1450 ± 70)/ T ] and (1.59 ± 0.41) × 10 –12 exp[–(1470 ± 80)/ T ] cm 3 molecule –1 s –1 at 253–328 K. At 298 K, k 3 and k 4 were deduced to be (1.71 ± 0.32) × 10 –14 and (1.67 ± 0.19) × 10 –14 cm 3 molecule –1 s –1 . The observed products of the reaction of n -C 4 F 9 OCH 3 with OH radicals were n -C 4 F 9 OC(O)H, CF 3 CF 2 CF 2 C(O)F, and COF 2 , and those for the reaction of i -C 4 F 9 OCH 3 were i -C 4 F 9 OC(O)H, (CF 3 ) 2 CFC(O)F, CF 3 C(O)F, and COF 2 .

The atmospheric chemistry of CF 3 (CF 2 ) 7 H was studied in an 11.5-dm 3 environmental reaction chamber by means of Fourier transform infrared spectroscopy. Using a relative rate method, we determined the Arrhenius expression for the rate constant of the reaction of CF 3 (CF 2 ) 7 H with OH radicals to be (4.32 ± 1.87) × 10 –13 exp[–(1540 ± 130)/ T ] cm 3 mol –1 s –1 at 253 – 328 K. At 298 K, COF 2 was a sole product in a molar yield of (1.02 ± 0.11) in terms of carbon.

Rate constants for the reactions of OH and NO3 radicals with CH2CHF (k1 and k4), CH2CF2 (k2 and k5), and CHFCF2 (k3 and k6) were determined by means of a relative rate method. The rate constants for OH radical reactions at 253–328 K were k1 = (1.20 ± 0.37) × 10−12 exp[(410 ± 90)/T], k2 = (1.51 ± 0.37) × 10−12 exp[(190 ± 70)/T], and k3 = (2.53 ± 0.60) × 10−12 exp[(340 ± 70)/T] cm3 molecule−1 s−1. The rate constants for NO3 radical reactions at 298 K were k4 = (1.78 ± 0.12) × 10−16 (CH2CHF), k5 = (1.23 ± 0.02) × 10−16 (CH2CF2), and k6 = (1.86 ± 0.09) × 10−16 (CHFCF2) cm3 molecule−1 s−1. The rate constants for O3 reactions with CH2CHF (k7), CH2CF2 (k8), and CHFCF2 (k9) were determined by means of an absolute rate method: k7 = (1.52 ± 0.22) × 10−15 exp[−(2280 ± 40)/T], k8 = (4.91 ± 2.30) × 10−16 exp[−(3360 ± 130)/T], and k9 = (5.70 ± 4.04) × 10−16 exp[−(2580 ± 200)/T] cm3 molecule−1 s−1 at 236–308 K. The errors reported are ±2 standard deviations and represent precision only. The tropospheric lifetimes of CH2CHF, CH2CF2, and CHFCF2 with respect to reaction with OH radicals, NO3 radicals, and O3 were calculated to be 2.3, 4.4, and 1.6 days, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 619–628, 2010

The structures of iminium salts formed from diarylprolinol or imidazolidinone derivatives and α,β-unsaturated aldehydes have been studied by X-ray powder diffraction (Fig. 1), single-crystal X-ray analyses (Table 1), NMR spectroscopy (Tables 2 and 3, Figs. 2–7), and DFT calculations (Helv. Chim. Acta2009, 92, 1, 1225, 2010, 93, 1; Angew. Chem., Int. Ed.2009, 48, 3065). Almost all iminium salts of this type exist in solution as diastereoisomeric mixtures with (E)- and (Z)-configured +NC bond geometries. In this study, (E)/(Z) ratios ranging from 88 : 12 up to 98 : 2 (Tables 2 and 3) and (E)/(Z) interconversions (Figs. 2–7) were observed. Furthermore, the relative rates, at which the (E)- and (Z)-isomers are formed from ammonium salts and α,β-unsaturated aldehydes, were found to differ from the (E)/(Z) equilibrium ratio in at least two cases (Figs. 4 and 5, a, and Fig. 6, a); more (Z)-isomer is formed kinetically than corresponding to its equilibrium fraction. Given that the enantiomeric product ratios observed in reactions mediated by organocatalysts of this type are often ≥99 : 1, the (E)-iminium-ion intermediates are proposed to react with nucleophiles faster than the (Z)-isomers (Scheme 5 and Fig. 8). Possible reasons for the higher reactivity of (E)-iminium ions (Figs. 8 and 9) and for the kinetic preference of (Z)-iminium-ion formation are discussed (Scheme 4). The results of related density functional theory (DFT) calculations are also reported (Figs. 10–13 and Table 4).

Rate constants for reactions of erythro- CF 3 CHFCHFC 2 F 5 and threo- CF 3 CHFCHFC 2 F 5 with OH radicals were determined by means of a relative rate method in an 11.5-dm 3 reaction chamber at 253 – 328 K: k 1 ( erythro -CF 3 CHFCHFC 2 F 5 + OH) = (9.60 ± 3.39) × 10 –13 exp[–(1680 ± 100)/ T ] and k 2 ( threo -CF 3 CHFCHFC 2 F 5 + OH) = (6.60 ± 2.06) × 10 –13 exp[–(1580 ± 90)/ T ] cm 3 molecule –1 s –1 .

Rate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo-CF2CF2CHFCH2(k1), trans-cyclo-CF2CF2CHClCHF(k2), cyclo-CF2CFClCH2CH2(k3), trans-cyclo-CF2CFClCHClCH2(k4), and cis-cyclo-CF2CFClCHClCH2(k5) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H2OO3O2He gas mixture in an 11.5-dm3 temperature-controlled reaction chamber. Rate constants of k1 = (5.52 ± 1.32) × 10−13 exp[–(1050 ± 70)/T], k2 = (3.37 ± 0.88) × 10−13 exp[–(850 ± 80)/T], k3 = (9.54 ± 4.34) × 10−13 exp[–(1000 ± 140)/T], k4 = (5.47 ± 0.90) × 10−13 exp[–(720 ± 50)/T], and k5 = (5.21 ± 0.88) × 10−13 exp[–(630 ± 50)/T] cm3 molecule−1 s−1 were obtained at 253–328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%–15% uncertainty to the uncertainty of k1–k5. The reactivity trends of these OH radical reactions were analyzed by using a collision theory–based kinetic equation. The rate constants k1–k5 as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their CH bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo-CF2CF2CHFCH2, trans-cyclo-CF2CF2CHClCHF, cyclo-CF2CFClCH2CH2, trans-cyclo-CF2CFClCHClCH2, and cis-cyclo-CF2CFClCHClCH2, respectively, by scaling from the lifetime of CH3CCl3. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532–542, 2009

Structures of the reactive intermediates (enamines and iminium ions) of organocatalysis with diarylprolinol derivatives have been determined. To this end, diarylprolinol methyl and silyl ethers, 1, and aldehydes, PhCH2CHO, tBuCH2CHO, PhCH=CHCHO, are condensed to the corresponding enamines, A and 3 (Scheme 2), and cinnamoylidene iminium salts, B and 4 (Scheme 3). These are isolated and fully characterized by melting/decomposition points, [α]D, elemental analysis, IR and NMR spectroscopy, and high-resolution mass spectrometry (HR-MS). Salts with BF4, PF6, SbF6, and the weakly coordinating Al[OC(CF3)3]4 anion were prepared. X-Ray crystal structures of an enamine and of six iminium salts have been obtained and are described herein (Figs. 2 and 4–8, and Tables 2 and 7) and in a previous preliminary communication (Helv. Chim. Acta2008, 91, 1999). According to the NMR spectra (in CDCl3, (D6)DMSO, (D6)acetone, or CD3OD; Table 1), the major isomers 4 of the iminium salts have (E)-configuration of the exocyclic NC(1′) bond, but there are up to 11% of the (Z)-isomer present in these solutions (Fig. 1). In all crystal structures, the iminium ions have (E)-configuration, and the conformation around the exocyclic N-CC-O bond is synclinal-exo (cf.C and L), with one of the phenyl groups over the pyrrolidine ring, and the RO group over the π-system. One of the meta-substituents (Me in 4b, CF3 in 4c and 4e) on a 3,5-disubstituted phenyl group is also located in the space above the π-system. DFT Calculations at various levels of theory (Tables 3–6) confirm that the experimentally determined structures (cf. Fig. 10) are by far (up to 8.3 kcal/mol) the most stable ones. Implications of the results with respect to the mechanism of organocatalysis by diarylprolinol derivatives are discussed.

The stable geometries of fucose-benzene complex and the stabilization energies by formation of the complex (E(form)) were studied by ab initio molecular orbital calculations. The benzene ring has close contact with an O-H or C-H bond of fucose in the optimized geometries (OH/pi hydrogen-bonded structures and CH/pi contact structures). The E(form) calculated for the most stable OH/pi hydrogen-bonded structure was -5.1 kcal/mol. The E(form) calculated for the most stable CH/pi contact structure was -4.5 kcal/mol, which shows that significant attraction exists between the nonpolar surface of fucose and a benzene. The E(form) is close to the interaction energies in typical hydrogen-bonded complexes. A few nearly isoenergetic CH/pi contact structures were found by the calculations, which suggests that the directionality of the carbohydrate-aromatic interaction is weak. The dispersion interaction is the major source of the attraction in the complex. The electrostatic contributions to the attraction are relatively small. Although the size of the interaction energy is not largely different from that of typical hydrogen bonds, the nature of the carbohydrate-aromatic interaction, which is sometimes denoted as a CH/pi hydrogen bond, is completely different from that of typical hydrogen bonds, which have strong directionality due to the strong electrostatic interactions.

The reaction of cinnamaldehyde with cyclopentadiene in the presence of DPPL as catalyst leads to substituted cyclopentadiene Michael-type adducts (III) and (IV), whilst the reaction with DTFP catalyst affords Diels—Alder adducts (V) and (VI).

The first step in the title reaction proceeds with good to excellent enantioselectivity and the cis-isomer is generally the major one.

Palladium (Pd) generally prefers low oxidation states. So far, no stable Pd compound with a +5 oxidation state is known. Here, we report two multinuclear Pd compounds containing Pd centers ligated by five silicon (Si) atoms. A thermal condensation reaction of [{1,2-C 6 H 4 (SiMe 2 )(SiH 2 )}Pd II (Me 2 PCH 2 CH 2 PMe 2 )] (Me = methyl) afforded two stereoisomers of dinuclear Pd II compounds and a trinuclear Pd compound as major products and a tetranuclear Pd compound as a minor product. The structures of the four Pd compounds were confirmed by single-crystal x-ray structure analysis. The dinuclear Pd compounds have a dimeric structure of [{1,2-C 6 H 4 (SiMe 2 )(SiH)}Pd II (Me 2 PCH 2 CH 2 PMe 2 )] connected through a Si–Si single bond formed by dehydrogenation of two molecules of the starting compound. The trinuclear and tetranuclear Pd compounds proved to have Pd centers bonded to five Si atoms with normal Pd–Si single-bond distances. Theoretical calculations of the trinuclear and tetranuclear Pd compounds accurately reproduced their x-ray structures and suggested that all of the Pd–Si bonds of the central Pd atoms have a relatively high single-bond character.

This paper describes the results of ab initio investigations on the reactions of OH radical/O (3P) atom addition to halogen-substituted ethenes (CH2 CHX, CH2 CX2; X=F, Cl, Br) and propene. Two reaction pathways, addition to the substituted carbon atom (α-site) and addition to the non-substituted carbon atom (β-site), have been examined. The energetic of each reaction coordinate has been evaluated at the computational level of PMP2/aug-cc-pVTZ//MP2/6-311+G(2d,p). Our calculations suggested that the reactions of OH radical addition should be more exothermic than those of the O (3P) atom addition and that the α-addition products should be lower in energy than the corresponding β-addition products. Relative stabilities of the transition states for the α- and β-addition channels can be discussed in terms of the exothermicities of the reaction channels and the relative spin densities in the 3ππ* states of the reactant ethene molecules. For the reactions of the chloro- and bromo-substituted ethenes, the transition states for the α-addition were found to be higher in energy than those for the β-addition, but for the reactions of the fluoro-substituted ethenes and propene, the differences in energy between the transition states for the α- and β-addition channels were found to be rather small.

It is widely known that addition of a radical species to the sulfur atom of a reduced sulfur molecule results in formation of a two-center three-electron (2c-3e) bond, but relatively few investigations have been reported for the 2c-3e bond between the NO3 radical and a sulfur molecule. This article presents results of gas-phase DFT and ab initio investigations on the 2c-3e type adducts of the NO3 radical with reduced sulfur molecules. By using correlation consistent basis sets, geometry optimizations at the MP2 and BH&HLYP levels and single-point energy evaluations at the CCSD(T) level were carried out. Our estimates for the dissociation enthalpies (ΔH (298 K)) of the 2c-3e S–O bonds in the NO3 radical adducts of the CH3SH, CH3SCH3, and CH3SSCH3 molecules are 7∼10, 15∼16, and 10∼12 kcal/mol, respectively, but our calculations suggest that the H2S molecule will not actually form a 2c-3e adduct with the NO3 radical.

The kinetics of CF 2 CF–CF CF 2 reaction with O 3 ( k 1 ) and NO 3 radicals ( k 2 ) were measured using a smog chamber/FTIR technique. The value of k 1 was determined as (1.14 ± 0.94) × 10 −16 exp [−(2800 ± 225)/ T ] in the range 225–308 K by means of an absolute rate method and k 2 was determined to be (1.5 ± 0.2) × 10 −15 cm 3 molecule −1 s −1 at 298 K by a relative rate method. The tropospheric lifetime of CF 2 CF–CF CF 2 was estimated at 6.3 and 0.8 years with respect to its reaction with O 3 and NO 3 radicals, respectively.

Henry's law constants of two fluorinated esters [CF3CH2OC(O)H and C2H5OC(O)CF3] and four related non-fluorinated esters [CH3OC(O)H, C2H5OC(O)H, n-C3H7OC(O)H and C2H5OC(O)CH3] were determined at 278–298 K by a column-stripping method. From the van’t Hoff equation of H = H 298 exp [ - Δ H sol R ( 1 T - 1 298 ) ] , the H298 (M atm−1) and ΔHsol (kJ mol−1) values obtained were 0.55±0.04, −39±3 (CF3CH2OC(O)H); 0.09±0.01, −41±5 (C2H5OC(O)CF3); 4.2±0.2, −33±2 (CH3OC(O)H); 3.4±0.2, −38±2 (C2H5OC(O)H); 2.6±0.1, −42±1 (n-C3H7OC(O)H); and 6.0±0.5, −49±3 (C2H5OC(O)CH3), respectively. Errors reported are at 95% confidence levels and represent precision only. Hydrolysis was observed only for C2H5OC(O)CF3. Replacement of CH3 by CF3 decreases H298 values by 6, 11, and 67 times, respectively, for CF3CH2OC(O)H, CF3CH2OC(O)CH3, and C2H5OC(O)CF3, while the differences in the ΔHsol values were small with these substitutions. Sodium chloride salting-out effects are examined for all of the esters. C2H5OC(O)CF3 has the largest salting coefficient (0.74). The estimated lifetime of CF3CH2OC(O)H suggests that dissolution into seawater serves as a tropospheric sink for this compound. On the basis of the solubility and reactivity of the esters studied herein, clouds and the ocean are discussed as possible sinks for the dissolution of tropospheric CF3CF2OC(O)H, which is an atmospheric oxidation product of a substitute for hydrofluorocarbons as CF3CF2OCH3.

In the proline-mediated Mannich and aldol reactions of propanal as a nucleophile, the aldimine prepared from benzaldehyde and p-anisidine is about 7 times more reactive than the corresponding alde- hyde, benzaldehyde, as an electrophile. This higher reactivity of aldimine over aldehyde is attributed to the carboxylic acid of proline protonating the basic ni- trogen atom of the aldimine more effectively than the oxygen atom of the aldehyde, an explanation which has been both experimentally and theoretically veri- fied.

Ab initio and DFT investigations on H 2 S–OH and (CH 3 ) 2 S–OH adducts have shown that electron correlation is essential for an accurate description of the two-center three-electron S–O bonds in the adducts. Calculations at the BH&HLYP, B3LYP, MP2, and CCSD(T) levels indicate that the S–O bond in the (CH 3 ) 2 S–OH adduct is considerably stronger and shorter than that in the H 2 S–OH adduct. Our best estimate for the dissociation enthalpy at 298 K for the S–O bond in the (CH 3 ) 2 S–OH adduct is 9.0 kcal/mol, which is in satisfactory agreement with experimentally derived values.