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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.

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.

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.

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 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.

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 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.

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.

Molecular interactions between pi systems having different pi-electron character (benzene, hexafluorobenzene, and borazine), and a Lewis acid/base (borane and ammonia) were theoretically studied. An attractive interaction between benzene, the electron-rich pi system, and borane was observed. On the other hand, repulsive interactions between benzene and ammonia was observed when the lone pair of nitrogen points toward the benzene ring. In contrast, an attractive interaction between hexafluorobenzene, an electron-deficient pi system, and ammonia was observed. Unexpectedly, a weak attractive interaction between hexafluorobenzene and borane was also observed. Borazine shows an interaction both to borane and ammonia. The attraction between the nitrogen atom of borazine and borane was larger than that between the boron atom of borazine and ammonia.

The electronic structures and energetics of the reactants, products, transition states, and association complexes involved in the reaction of dimethyl ether (DME) and dimethyl sulfide (DMS) with OH radical have been investigated at the MP2(FC) and DFT (BHH one represents a direct hydrogen-abstraction and the other one for the abstraction through prereactive complex. Among the computational levels employed in the present work, the PMP2/6-311++G(2df,2pd)//M2/6-311++G(d,p) level was found to reproduce best the experimentally measured rate constants. Our best estimates of the rate constants at 298 K for the reactions of OH radical with DME and DMS are 5.9×10−13 and 1.1×10−12 cm3 molecule−1 s−1, respectively, which are underestimated by 4 times as compared to the experimentally derived values. At low temperatures, the direct H-abstraction predominates over the H-abstraction through the prereactive complex, while both channels compete at elevated temperatures.

Intermolecular interaction energies of 12 orientations of C(3)F(8) dimers were calculated with electron correlation correction by the second-order Møller-Plesset perturbation method. The antiparallel C(2h) dimer has the largest interaction energy (-1.45 kcal/mol). Electron correlation correction increases the attraction considerably. Electrostatic energy is not large. Dispersion is mainly responsible for the attraction. Orientation dependence of the interaction energy of the C(3)F(8) dimer is substantially smaller than that of the C(3)H(8) dimer. The calculated interaction energy of the C(3)F(8) dimer at the potential minimum is 78% of that of the C(3)H(8) dimer (-1.85 kcal/mol), whereas the interaction energies of the CF(4) and C(2)F(6) dimers are larger than those of the CH(4) and C(2)H(6) dimers. The intermolecular separation in the C(3)F(8) dimer at the potential minimum is substantially larger than that in the C(3)H(8) dimer. The larger intermolecular separation due to the steric repulsion between fluorine atoms is the cause of the smaller interaction energy of the C(3)F(8) dimer at the potential minimum. The calculated intermolecular interaction energy potentials of the C(3)F(8) dimers using an all atom model OPLS-AA (OPLS all atom model) force field and a united atom model force field were compared with the ab initio calculations. Although the two force fields well reproduces the experimental vapor and liquid properties of perfluoroalkenes, the comparison shows that the united atom model underestimates the potential depth and orientation dependence of the interaction energy. The potentials obtained by the OPLS-AA force field are close to those obtained by the ab initio calculations.

Intermolecular interaction energies of n-butane, n-pentane, and n-hexane dimers were calculated at the MP2 level with a large basis set including multiple polarization functions. The comparison of ...

Ab initio investigations on the gas-phase reaction pathways for the hydrolytic decomposition of CF2O molecule have indicated that the energy barriers for the reaction channels of CF2O with a single H2O molecule are significantly reduced when an additional H2O molecule is brought into the reaction system. The additional H2O molecule serves as a proton relay acting simultaneously as a proton donor and acceptor in the transition states. These findings may imply that reaction channels in which multiple, at least two, H2O molecules participate will be important for the homogeneous gas-phase hydrolysis of CF2O.

A molecular interaction between a methane/fluoromethane molecule and a benzene/hexafluorobenzene molecule was theoretically studied. Attractive interaction between the fluorine atom of the fluoromethane and the π-system of the hexafluorobenzene was observed (C−F/πF interaction, −2.43 kcal/mol in MP2/aug-cc-pVDZ). The attractive C−F/πF interaction energy was larger than that of the interaction between methane and benzene (C−H/πH interaction, −1.47kcal/mol). On the other hand, the very weak repulsive interaction was observed between the fluorine atom of the fluoromethane and the benzene (C−F/πH interaction, +0.12 kcal/mol). The interaction energies between methane and benzene (C−H/πH interaction, −1.47 kcal/mol) and between methane and hexafluorobenzene (C−H/πF interaction, −1.36 kcal/mol) were almost the same.

We employed ab initio quantum mechanical techniques, such as HF, MP2, and QCISD methods, to explore the conformational spaces of fluoromethyl formate and difluoromethyl formate, HC(O)OCH 3 − n F n ( n =1,2). Three potential energy minima, two with the syn and one with the anti configuration, were located for fluoromethyl formate, while four potential energy minima, two with the syn and the other two with the anti configuration, were located for difluoromethyl formate. In addition, we characterized several rotational transition states for the rotation of the C–O single bond adjacent to the carbonyl group or that adjacent to the fluoro-substituted methyl group. The results of the energy evaluations of the rotational stationary points suggest that the syn / anti energy difference, as well as the barrier height to the syn / anti interconversion, tends to decrease monotonously on going from methyl formate to trifluoromethyl formate, via fluoromethyl formate and difluoromethyl formate.

The interaction energies of the alkaline-earth-metal dication/benzene complexes (dication = Mg 2 + and Ca 2 + ) were calculated at the MP2 (the second-order Moller-Plesset calculation) level using the 6-311G** basis set. The electrostatic and induction energies were calculated with the distributed multipoles and distributed polarizabilities model. Induction is mainly responsible for the very strong attractive interaction in these complexes. Electrostatic energies are considerably smaller than the induction energies. The complexes have significant attraction, even if the cations are well separated from the benzene, which indicates that short-range (covalent) interactions are not the major source of the attraction and that long-range interactions (induction and electrostatic interactions) are mainly responsible for the attraction. The calculations of benzene under an electric field show that the electric field produced by the dication is a cause of the C-C bond elongation in the alkaline-earth-metal dication/benzene complexes.

To investigate the fluorine substitution effect on the rate for ester hydrolysis, the energies of the tetrahedral intermediates, as well as those of the reactants and products, were evaluated with ab initio calculations. The CBS-4 and CBS-Q energies suggested significant acceleration of the hydrolysis rate of fluoro-substituted esters: not only the trifluoromethyl group in the acyl portion of esters but also that in the alcohol portion will accelerate significantly the ester hydrolysis rate as compared to non-substituted counterparts. This implies that perfluoroalkyl esters resulting from the atmospheric degradation of hydrofluoroethers (HFEs) will be rather unstable even in almost neutral hydrolytic conditions.

This article describes an ab initio investigation on the potential surfaces for one of the simplest hydrogen atom abstraction reactions, that is, HO + H2O ↔ H2O + OH. In accord with the findings in the previously reported theoretical investigations, two types of the hydrogen-bonding complexes [HOHOH] and [H2OHO] were located on the potential energy surface. The water molecule acts as a hydrogen donor in the [HOHOH] complex, while the OH radical acts as a hydrogen donor in the [H2OHO] complex. The energy evaluations at the MP2(FC) basis set limit, as well as those through the CBS-APNO procedure, have provided estimates for enthalpies of association for these complexes at 298 K as −2.1 ≈ −2.3 and −4.1 ≈ −4.3 kcal/mol, respectively. The IRC calculations have suggested that the [H2OHO] complex should be located along the reaction coordinate for the hydrogen abstraction. Our best estimate for the classical barrier height for the hydrogen abstraction is 7.8 kcal/mol, which was obtained from the CBS-APNO energy evaluations. After fitting the CBS-APNO potential energy curve to a symmetrical Eckart function, the rate constants were calculated by using the transition state theory including the tunneling correction. Our estimates for the Arrhenius parameters in the temperature region from 300 to 420 K show quite reasonable agreement with the experimentally derived values. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1538–1548, 2003

The rate constants for the hydrogen abstraction reaction of hydrofluoroethers (HFEs) and hydrofluorocarbons (HFCs) with OH radicals (kOH) at 298 K were estimated by using new empirical estimation method consisting of two steps. Firstly we calculated the bond dissociation enthalpies (BDEs) of the C–H bond by using the artificial neural network (ANN) technique from molecular formula. Next, kOH were evaluated by using the estimated BDEs and a modified Heicklen’s empirical equation. Consequently, the combination of these two empirical methods could estimate the kOH of HFEs and HFCs within the 0.56–1.8 times of experimental data as average deviation.

The energy profile of the interconversion path between the T-shape and slipped-parallel dimers has been studied by high level ab initio calculations. The CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the MP2 (the second-order Moller–Plesset calculation) interaction energy near the basis set limit and the CCSD(T) correction term using the 6-311G* basis set. The calculated CCSD(T) level energy profile has shown that the potential is very flat and the interconversion barrier height is very small (around 0.2 kcal/mol). The MP2 calculations using large basis sets near the basis set limit considerably overestimate the attraction of the slipped-parallel dimer, which indicates the importance of higher level electron correlation correction for studying the potential energy surface of the benzene dimer.

The three-layered feed-forward type artificial neural network (ANN) was applied to estimate the bond dissociation enthalpies (BDEs) of the C–H bonds in partially halogenated alkanes and ethers. The training values consisted of BDEs of the 93 C–H bonds in 53 alkanes and 24 ether molecules, which were computed by using density functional theory at the (RO)B3LYP/6-311G ∗∗ level. As input parameters of ANN, we defined 14 kinds of topological descriptors, such as H–C⋯X (X=H, F, Cl, Br, O), H–C–C⋯X (X=H, F, Cl, O), H–C–C–C⋯X (X=H, F, O), H–C–O–C⋯X (X=H, F). Consequently, the average of absolute deviation in correlation and estimation were 0.70 and 0.84 kcal/mol, respectively. It was possible to construct a reliable and useful BDE estimation method.

Basis set effect in evaluation of base pair formation energy of the Watson–Crick type base pair between substituted 1-methyluracil and 9-methyladenine was studied in the Hartree–Fock and second-order Moller–Plesset level of theory. The same trend was observed in the substitution effect in all basis sets attempted; thus, the error depending on the basis set incompleteness is minimal in the evaluation of the substitution effect of the base pair formation energy. Neither the hydrogen bond distance nor the atomic charge was a valid index for the hydrogen bond status in base pairing.

The proton affinity (PA) of the oxygen atoms and the deprotonation enthalpies (DPE) of the NH bonds of 5-substituted uracil derivatives ( X =CN, F, Cl, NH 2 ) are computed using the density functional theory (B3LYP) at the 6-31+G(d,p) level. The PAs vary from 766 to 875 kJ mol −1 and the DPEs from 1315 to 1442 kJ mol −1 . For all the studied uracils, the acidity of the N1H bond is larger than that of the N3H bond and the basicity of the O8 atom is larger than that of the O4 atom. The effect of the intramolecular hydrogen bond in 5-NH 2 uracil is discussed. The three stable complexes with one water molecule are the ones in which the oxygen atom of water accepts the acidic NH proton while donating a proton to the carbonyl oxygen of uracils. The intermolecular distances and angles, and the binding energies with water are discussed in terms of the PA and DPE of the atoms or bonds involved in the interaction with one water molecule.

The 1,3-dipolar cycloadditions of nitrous oxide and substituted alkynes have been studied at the B3LYP/6-31G(d,p) level. The reaction is controlled by LUMO (dipole)--HOMO (dipolarofile) and involves aromatic transition structures. The shape of the potential energy surface and the regioselectivity are not affected by the polarity of the solvents, except in the case of N2O + HC triple bond CSiH3. Different reactivity criteria including FMO coefficients product C, local softness differences Delta, magnetic susceptibility anisotropy chi(anis), and nucleus-independent chemical shifts NICS were used to predict the regioselectivity in all studied cases; the C, Delta criteria turn out to give the best results among them. The aromaticity of the transition structure is not a factor in determining the regiochemistry of the cycloaddtition reactions.

The hydrogen abstraction reactions of 1,1- and 1,2-difluoroethane with the OH radical have been investigated by the ab initio molecular orbital theory. The geometries of the reactants, products, and transition states have been optimized at the (U)MP2=full level of theory in conjunction with 6-311G(d,p) basis functions. Single-point (U)MP2=full with larger basis set, such as 6-311G(3d,2p), and QCISD(T)=full/6-311G(d,p) calculations have also been carried out to observe the effects of basis sets utilized and higher order electron correlation. Three and four reaction channels have been identified for 1,1- and 1,2-difluoroethane, respectively. In the case of 1,1-difluoroethane, hydrogen abstraction from the α-carbon has been found to be easier than that from the β-carbon. The barriers of the four reaction channels for 1,2-difluoroethane are close to each other. Weak hydrogen bonding interactions have been observed between hydroxyl hydrogen and a fluorine atom in the transition states. Rate constants for the reactions of 1,1- and 1,2-difluoroethane with the OH radical have been calculated using the standard transition state theory and found to be in good agreement with the experimental results. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1305–1318, 2000

Photolyses of 1,2;4,5- and 1,2;3,4-benzenetetracarboxylic dianhydrides (3a and 3b), which would be precursors of 1,4- and 1,3-benzdiyne (2a and 2b), were studied by a matrix isolation technique and a selective irradiation technique using three kinds of excimer lasers in order to directly observe intermediates produced stepwise. The photolyzed products in the matrix were characterized by FT-IR and UV–vis spectroscopies. As a result, sequential decarboxylation and decarbonylation from one anhydride moiety of 3a and 3b produced corresponding benzocyclopropenone and benzyne intermediates in the initial stage. In both the photolyses, further decomposition proceeded to form 1,3,5-hexatriyne (4) as a final product. Although neither 2a nor 2b was observed directly, it seems that the benzdiynes including another isomer, 1,2,3,5-tetradehydrobenzene (2c), participated as precursors to acyclic C4H–Câ–·C–H biradical 13 and/or carbene 14, which were formed in the reaction from benzdiyne to 4. Additionally, as a result of CCSD(T)/6-31G**//CASSCF(4,4)/6-31G** level calculations for 2a, 2b and 2c, it is clear that the energy of 2c was comparable to those of 2a and 2b, which supports the formation of 13 from 2a/2b and of 14 from 2c after isomerization of 2a→2c and 2b→2c.

The energy profile of the lowest energy path connecting the slipped parallel (C2h) and T-shaped (C2v) dimers of carbon dioxide was investigated using a reasonably large 6-311+G(2df) basis set with the MP2 level electron correlation correction and with the counterpoise correction. There was no inversion barrier and the T-shaped dimer was a transition state connecting the two slipped parallel dimers. The calculated interaction energies of the two dimers (−1.290 and −1.072 kcal/mol) were larger than those reported previously. The calculated energy difference of the two dimers (0.218 kcal/mol) was also larger than the previous values (less than 0.1 kcal/mol). The effects of basis set, electron correlation, and basis set superposition error were studied in detail. The second-order Mo/ller–Plesset (MP2) interaction energies of the two dimers were close to the coupled cluster calculations using single and double substitutions including noniteratively triple excitations [CCSD(T)] ones. The choice of the basis set...

Properties of various oxyphosphoranes such as neutral pentahydroxyphosphorane (doubly protonated 3b) and dianionic trihydroxyphosphorane (3b) and trimethoxyphosphorane (3a) were examined by ab initio molecular orbital calculations. The energies of the stationary points were evaluated at the MP2 level of theory with the 6-31+G * basis. The analysis of the oxyphosphorane species indicates that the orientation of the equatorial methoxyl group determines the mode of formation/cleavage of the axial P-O 2 /P-O 5 bond. This dependence of the reactivity on the conformation of the equatorial P-O 3 bond is in accord with the prediction that is based on the stereoelectronic effect

The efficient asymmetric total synthesis of (―)-oseltamivir, an antiviral reagent, has been accomplished by using two "one-pot" reaction sequences, with excellent overall yield (60 % ) and only one required purification by column chromatography. The first one-pot reaction sequence consists of a diphenylprolinol silyl ether mediated asymmetric Michael reaction, a domino Michael reaction/ Horner―Wadsworth―Emmons reaction combined with retro-aldol/Horner― Wadsworth―Emmons reaction and retro Michael reactions, a thiol Michael reaction, and a base-catalyzed isomerization. Six reactions can be successfully conducted in the second one-pot reaction sequence; these are deprotection of a tert-butyl ester and its conversion into an acyl chloride then an acyl azide, Curtius rearrangement, amide formation, reduction of a nitro group into an amine, and a retro Michael reaction of a thiol moiety. A column-free synthesis of (—)—oseltamivir has also been established.

Hydrogen bond complex stability between adenine (A) and hydrogen bond equivalents of uracil: 2-pyridone derivatives (U(X2O)X) and 3-oxo-1,2,6-thiadiazine-1,1-dioxide derivatives (U(SO2)X) was studied, and as the result, the hydrogen bond energy of U(X2O)X-A and a complex of UX(SO2)X-A, was about 1.5 kcal/mol more stable than that of the corresponding adenine-uracil derivatives complex, respectively. The energy difference between the imide tautomer and enol tautomer was smaller than those of uracil derivatives. U(SO2)F can form a stable complex with A, and its imide tautomer is stable.

Multistep fluorescence resonance energy transfer in a system containing three chromophores is dependent upon the relative arrangement of the chromophore triad.