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We have examined the energy components of hydrogen-bonding interactions by using self-consistent charge and configuration method for subsystems (SCCCMS) and charge sensitivity parameters. Our procedure indicated that the main source of the stabilization for hydrogen-bonding association was the electrostatic contribution. The secondary electrostatic and polarization interactions due to polar functional groups located closely to the hydrogen-bonding sites were shown to significantly alter the magnitude of hydrogen-bonding stabilization. This finding supports Jorgensen and co-workers' interpretation toward the hydrogen-bonding energies [e.g., W.L. Jorgensen, D.L. Severance, J. Am. Chem. Soc. 113 (1991) 209].

The density functional theory based descriptor of reactivity, hardness, correlates well with the activation energies for a series of hydrogen atom abstraction reactions between the hydroxyl radical and halomethane compounds. A good correlation has also been observed for simple haloethane compounds.

The charge-transfer energy in water dimer is analyzed. The analysis is based on self-consistent charge and configuration method for subsystems (SCCCMS). The SCCCMS, as such, is not restricted to any computational schemes and can be applied at Hartree–Fock (HF), post-HF, and density functional levels of theory. In our approach, the interaction energy is decomposed into deformation (DEF), electrostatic (ES), polarization (P), charge transfer (CT), and exchange (EX) [exchange–correlation (XC)] contributions. The CT energy is derived from the energy surface spanned in the populational space. The intermediate results obtained during construction of this energy surface, such as chemical potentials, hardness and softness parameters, are of particular interest in the theory of chemical reactivity and, thus, these values are discussed as well. The influence of basis set and computational method is analyzed. The numerical values of the energy components obtained at the HF level of theory are compared with those of ...

The basis set effect in evaluation of hydrogen bond energies of the Watson–Crick type base pairs between adenine (A) and uracil (U) and between guanine (G) and cytosine (C) was studied from 6-31G to 6-311++G(3df,p) basis set at the second-order Moller–Plesset (MP2) levels of theory using the structures optimized at the Hartree–Fock (HF) level of theory. Both the optimized structures around the hydrogen bonds and the hydrogen bond energies fluctuated largely depending on whether or not one set of the d-type polarization functions was set on the heavy atoms. The effects of the second and third sets of the d-type and first set of f-type polarization functions on the heavy atoms were smaller. Almost the same tendency was observed in the A–U and the G–C base pairs in the fluctuation of hydrogen bond energy depending on the basis set. The hydrogen bond energies of A–U and G–C base pairs calculated at MP2/6-31+(2d′,p′)//HF/6-31G(d,p) were in good agreement with the result of MP2/6-311++G(3df,p)//HF/6-311++G(3d,p).

The hydrogen abstraction reactions by OH radical from 1,1-dichloroethane and 1,2-dichloroethane have been investigated by ab initio molecular orbital theory. Optimized geometries and harmonic vibrational frequencies have been calculated for all reactants, transition structures, and products at the (U)HF/6-311G(d,p) and (U)MP2=full/6-311G(d,p) levels of theory. Single point QCISD(T)/6-311G(d,p)//(U)MP2=full/6-311G(d,p) calculations have also been carried out for the inclusion of higher order electron correlation. Three distinct transition structures have been located for the H3C−CHCl2 + OH reaction (one for α-abstraction and two for β-abstraction). Four transition structures have been located for the reaction ClH2C-CH2Cl + OH. The calculated barrier heights, reaction enthalpies, and change in entropy are found to be in good agreement with available experimental values. In addition, the rate constants calculated by using the transition state theory are found to be in good agreement with the experimental res...

The optimized geometries, harmonic vibrational frequencies, and energies of the cyclic structures of monohydrated guanine and adenine are computed using density functional theory (B3LYP) combined with the 6-31+G(d,p) basis set. The proton affinity of the O and N atoms and the deprotonation enthalpy of the different NH bonds of guanine and adenine are computed at the same level of theory. The results are compared with recent data on uracil, thymine, and cytosine. The intrinsic acidities and basicities of the five nucleobases are discussed. Complex formation with water results in a moderate change of the pyramidal character of the amino group. For closed complexes where water interacts with the O atom of the nucleobase, the intermolecular distances and the hydrogen bond energies are correlated to the proton affinities and deprotonation enthalpies of the sites involved in complex formation.

Systematic substituent effects on the stability of the hydrogen bonding between 9-methyladenine (A) and 1-methyluracil derivatives (UX) having various substituent groups were studied. The hydrogen bond stability of mismatched base pairs between 9-methylguanine (G) and the tautomeric enol structures (UX‘) of UX was also estimated. Geometry optimization of these bases and their base pairs using the 6-31G* basis set was carried out by Hartree−Fock (HF) self-consistent field (SCF) and the density functional theory (DFT) using Becke's three-parameter hybrid method with Predew/Wang 91 expression (B3PW91). The strength of hydrogen bonding was evaluated at the HF level and the second-order Moller−Plesset correlation energy correction (MP2) level in some cases. The calculated values for the hydrogen bonding strength using DFT were situated between those obtained by using HF and MP2 but closer to the latter than the former. Introduction of an electron-withdrawing group (EWG) into the uracil ring resulted in the for...

Intermolecular interaction energies of five C2H4−CH4 dimers and two C2H6-CH4 dimers were calculated. Dunning's correlation consistent basis sets (cc-pVXZ, X = D, T, Q, and 5) were used to estimate the MP2 interaction energies of the dimers at the basis set limit. The dimer in which the C−H bond of CH4 points to the CC bond of C2H4 has slightly larger bonding energy than the other four C2H4−CH4 dimers. The estimated CCSD(T) interaction energy of this dimer at the basis set limit is −0.49 kcal/mol, which is about 10% of the bonding energy of water dimer. The large correlation interaction energy (−0.86 kcal/mol), calculated as the difference between the HF and post-SCF interaction energies, suggests that the dispersion interaction is significantly important for the attraction between C2H4 and CH4. The analysis of the electrostatic interaction using distributed multipoles shows that the attractive electrostatic interaction (−0.24 kcal/mol) is playing important role to stabilize this dimer. On the other hand, ...

We present results of solution-phase ab initio and DFT investigations on the trigonal bipyramidal (TBP) intermediates postulated for the hydrolysis of methyl ethylene phosphate (MEP). A key intermediate for the hydrolysis would not be a TBP species with the hydroxyl group axial, but would be a TBP intermediate with the hydroxyl group equatorial. Considering the reaction pathways through this intermediate, not only exclusive ring opening in the dilute alkaline hydrolysis of MEP but also significant amount of exocyclic cleavage in the strong alkali can be rationalized. This interpretation is in accord with the mechanisms proposed by Lim et al. and by Lonnberg et al.

The MP2 intermolecular interaction energies of the title complexes were calculated with the Dunning’s correlation consistent basis sets (cc-pVXZ, X=D, T, Q, and 5) and the interaction energies at the basis set limit were estimated. The second-order Mo/ller–Plesset (MP2) interaction energies greatly depend on the basis sets used, while the Hartree–Fock (HF) energies do not. Small basis sets considerably underestimate the attractive interaction. The coupled cluster single double triple [CCSD(T)] interaction energies are close to the MP2 ones. The expected CCSD(T) interaction energies of the H2O–MeOH, H2O–Me2O, H2O–H2CO, MeOH–MeOH, and HCOOH–HCOOH complexes at the basis set limit are −4.90, −5.51, −5.17, −5.45, and −13.93 kcal/mol, respectively, while the HF/cc-pV5Z energies are −3.15, −2.58, −3.60, −2.69, and −11.29 kcal/mol, respectively. The HF calculations greatly underestimate the attractive energies and fail to predict the order of the bonding energies in these complexes. These results show that a large basis set and the consideration of an appropriate electron correlation correction are essential to study interactions of hydrogen bonding complexes by ab initio molecular orbital calculation.

The reactions of methane and hydrofluoromethanes (CH4-nFn, n = 0, 1, 2, or 3) with a hydroxyl radical have been investigated by a modified GAUSSIAN-2 (G2M) method. Reaction enthalpies have been compared to those obtained by original G2 and G2MP2 schemes. The average absolute error for the reaction enthalpies calculated with the G2M method was smaller than those calculated with the G2 and G2MP2 schemes. G2M reaction enthalpies were of chemical accuracy. Moreover, the G2M method and selected MP2 schemes (those with the smallest average errors in the calculations for the reaction enthalpies) were used to compute the classical barrier heights. According to the transition state theory, the reaction rates were computed in the temperature range of 280−420 K and then the activation energies were obtained by the least-squares fitting to the Arrhenius equation. The activation energies calculated by using G2M barrier heights showed the best agreement with the experimentally derived values. The influence of the fluor...

Transport abilities of alkaline earth, transition, and heavy metal ions were examined for three kinds of disubstituted monoacid derivatives of Kemp’s triacid as transport agents for a liquid membrane system. Diamide derivatives showed high transport ability for CaII over MgII, with selectivity ratios greater than 25. Imide monoacids were also CaII selective. For transition and heavy metal ions, all monoacids including diester monoacid showed very high HgII transport, but with different selectivities depending on the functional group. High HgII/AgI ( = 24), HgII/CuII ( = 194), and HgII/PbII ( = 85) selectivities were observed for diamide, diester, and imide monoacids, respectively. The transport mechanisms are discussed for alkaline earth, transition, and heavy metal ions utilizing ion chromatography analysis of anions co-transported.

The internal rotational barrier heights of biphenyl were calculated with the Dunning correlation consisted basis sets (up to cc-pVQZ, 960 basis functions) and the electron correlation correction by the second order Mo/ller-Plesset method (MP2). Although previous Hartree–Fock (HF) and MP2 calculations showed that the internal rotational barrier height at 0° (ΔE0) was substantially larger than that at 90° (ΔE90), our MP2/cc-pVQZ//MP2/6-31G* calculations showed that ΔE0 (2.28 kcal/mol) was close to ΔE90 (2.13 kcal/mol), which agreed with the estimation from experimental measurements. The calculations of benzene dimers suggested that the dispersion interaction increased the relative stability of the coplanar conformer. The basis sets employed in the previous calculations were not large enough to evaluate the attractive dispersion interaction. The underestimation of the stabilization of the coplanar conformer by the dispersion interaction would be one of the reasons for the overestimation of ΔE0 in the previous calculations.

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 cycloaddition reactions of 1,3-dipoles such as the simple azides (R–N3, R = H, CH3) with substituted ethylenes (H2CCHX, X = H, F, Cl, CH3, OH and CN) as dipolarophiles have been studied by a density functional procedure using the hybrid B3LYP exchange correlation functional and 6-31G(d,p) basis functions. For each system, two distinct transition states have been located corresponding to the relative orientation of two molecules. The energy difference between the two transition states varies from 0.2 to 5 kcal mol–1. The addition thus shows a certain regioselectivity. This observed regiochemistry is explained using recently developed DFT-based reactivity descriptors, such as local softness and Fukui functions.

The Fukui function is one of the most important concepts in the theory of chemical reactivity. For the fixed positions of nuclei, it describes reorganization in electron density of a given molecule due to overall chemical oxidation/reduction. The concept of the Fukui function was extended to reactive systems, giving a real two-reactant description of the chemical reaction. In this paper, the finite-difference approach was adopted to derive formulas for diagonal and off-diagonal Fukui functions in local and in atoms-in-molecule resolutions. The obtained results generalize the approach of Parr and Yang or Yang and Mortier into reactive systems, e.g. interacting molecules. The self-consistent charge and configuration method for subsystems (SCCCMS) was applied to calculate these quantities. A combination of Becke's three-parameter hybrid functional and the Perdew/Wang 91 gradient-corrected functional with the 6-31G* basis set was used in Kohn−Sham calculations. Methyl radical addition to ethylene was taken as...

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...

The self-consistent charge and configuration method for subsystems (SCCCMS), charge sensitivity analysis, and our new scheme for energy partitioning were applied to discuss the mechanism of addition of fluoromethyl radicals to fluoroethylenes. A hybrid density functional method, i.e., the combination of Becke's three-parameter functional and the Perdew/Wang 91 gradient-corrected functional, was used in the calculations with the 6-31G* basis set. Charge sensitivity characteristics (chemical potentials and hardnesses) of the reactants have been obtained. Chemical potentials clearly showed that alkenes act as donors of electrons (bases), while radicals act as acceptors (acids). The systems “electronic activation energies” were decomposed into deformation, electrostatic, polarization, charge-transfer, and exchange components. Steric effect was identified with the sum of deformation and exchange energies, while polar effect was related to the sum of electrostatic, charge-transfer, and polarization contribution...

Intermolecular interaction potentials of methane and ethylene dimers were calculated by the Hartree–Fock, Moller–Plesset, coupled cluster and density functional methods. The CCSD(T) electron correlation energies were close to the MP4(SDTQ) ones. The MP2 and MP3 energies were not largely different from the MP4(SDTQ) ones. On the other hand the CCSD and MP4(SDQ) methods largely underestimated the electron correlation energies. Dispersion interaction was not covered by the density functional methods using the BLYP, BPW91 and B3LYP functionals. These functionals also had defects in the evaluation of the repulsion interactions.

Medium-size basis sets were proposed to evaluate efficiently the dispersion interactions of hydrocarbon molecules. The aug(d,p)-6-311G** basis set was prepared by the augmentation of the diffuse d and p functions (αd(C) = 0.1565 and αp(H) = 0.1875) to the 6-311G** basis set. The aug(df,pd)-6-311G** basis set was prepared by the further augmentation of the diffuse f and d functions (αf(C) = 0.2 and αd(H) = 0.25) to the aug(d,p)-6-311G** basis set. The calculated MP2 and CCSD(T) intermolecular interaction energies of methane, ethane, propane, ethylene, acetylene, and benzene dimers with these basis sets were compared with those calculated with Sadlej's basis set and Dunning's correlation-consistent basis sets. Although the aug(d,p)-6-311G** basis set was more compact than Sadlej's basis set, this basis set was more effective to evaluate the dispersion energy. The aug(df,pd)-6-311G** basis set was considerably smaller than Dunning's cc-pVQZ and cc-pV5Z basis sets. The calculated interaction energies with the...

The intermolecular interaction potential of the corannulene dimer in a parallel (D5h) orientation was calculated by ab initio methods using basis sets up to 6-311G(2d) quality, with MP2 level electron correlation energy correction. The calculated potentials have their minima at a separation between the two five-membered rings of 3.2 A. An interaction energy of −13.39 kcal mol-1 was calculated at the MP2/6-311G(2d) level. The calculated electron correlation energy is −24.25 kcal mol-1, indicating that the dispersion interaction is the dominant term in the interaction of the corannulene dimer. The calculated potential in the repulsive region is less steep than those obtained from the Lennard-Jones type atom−atom potential parameters commonly used for the MD simulations of C60. It is suggested that the intermolecular interaction potential derived from the corranulene dimer will outperform atom−atom potentials for molecular dynamics studies of the bulk properties of fullerenes.

New derivatives of 1,3,5-trimethyl-r-1, c-3, c-5-cyclohexanetricarboxylic acid (Kemp’s triacid) showed high efficiency for alkaline earth and transition metal ion transport through a chloroform liquid membrane. Simple syntheses from Kemp’s triacid or its geometric isomer provided chelating agents with a tripodal binding site for metal cations. The tripodal binding site consisted of r-1, c-3-diaxial carboxyl group and a c-5-amide, ester, or C-methyl group. Alkaline earth metal transport was quite variable and sensitive to c-5-group changes. For transition metal transport, c-5-amide diacids gave high total transport efficiency. For c-5-ester or C-methyl diacids, complexation of smaller divalent cations was decreased, resulting in increased selectivity for large cations.

Ab initio investigations of the reaction profiles for the base-catalyzed methanolysis of amino-2-thiono-1,3,2-oxathiaphospholane suggested that ring opening with a retention of configuration at phosphorus would be energetically favorable, which provides a reasonable interpretation for the chemo- and stereoselectivity that have been determined experimentally for the reaction of diastereomerically pure 2-[(1-(α-naphthyl)ethyl)amino]-2-thiono-1,3,2-oxathiaphospholane. Nucleophilic attack at phosphorus will lead to a trigonal bipyramidal (TBP) pentacoordinate phosphorane intermediate, and pseudorotation will then occur concomitantly with collapse of the TBP intermediate. Thus, pseudorotation is strongly coupled with the reaction coordinate for the substitution pathway. This finding suggests that substitution with a retention of configuration can occur even though a TBP species resulting from pseudorotation fails to exist as an intermediate.

Chiral polycyclic aromatic hydrocarbons containing bis(1-adamantyl) groups at the peri-positions, named equatorenes, were synthesized in optically pure form starting from optically pure 4,5-bis(1-adamantyl)-8-methoxy-1-naphthol. A sequential Diels-Alder reaction of furan and arynes generated from 1,2-bromotriflates provided tricyclic and tetracyclic epoxides, and acid-catalyzed aromatization gave phenanthrol and chrysenol. Deoxygenation reactions involving the hydrogenolysis of triflates gave 1,8-bis(1-adamantyl)naphthalene, 1,10-bis(1-adamantyl)phenanthrene, and 1,12-bis(1-adamantyl)chrysene. 3,4-Bis(1-adamantyl)pyrene was synthesized from phenanthrol by Sonogashira coupling and Pt-catalyzed cyclization. Essentially no racemization occurred during the synthesis. X-ray analysis indicated the distorted naphthalene moiety possessing the peri-diadamantyl groups and the flat structure of the other benzene rings. UV-vis analysis of the equatorenes showed considerable redshifts compared with that of the corresponding achiral arenes. Electrochemical analysis of the naphthalene and pyrene indicated that the distortion decreased the highest occupied molecular orbital stability with no marked effect on the lowest unoccupied molecular orbital energy level, and the origin was discussed on the basis of calculation results.

The CCSD(T) level interaction energies at the basis set limit (E(int)) were calculated for 33 halogen bonded pyridine complexes with substituted iodobenzenes. The CCSD(T) level electron correlation correction substantially decreases the magnitude of attraction in comparison with the MP2. The E(int) for the pyridine complexes with mono substituted iodobenzenes varies from -3.14 to -4.42 kcal mol(-1), depending on the substituent. The electron-withdrawing substituents such as NO2 enhance the attraction, while the effects of electron-donating substituents reduce. The additivity of the substituent effects is observed for the E(int) of the pyridine complexes with multiple substituted iodobenzenes. The electrostatic interactions are mainly responsible for the substituent effects on the magnitude of the attraction in the halogen-bonded complexes. The electrostatic energy depends significantly on the substituent. They have a strong correlation with the E(int). On the other hand the effects of the substituent on the dispersion energy are small, however the dispersion does contribute greatly to the attraction.

Ab initio investigations on the reaction profiles for the base-catalyzed methanolysis of amino-2-thiono-1,3,2-oxathiophospholane suggested that the ring opening with retention of configuration at phosphorus would be energetically most favorable. This provides the rational interpretation for the chemo- and stereoselectivity ascertained experimentally for the reaction. The pseudorotation process is strongly coupled with the reaction coordinate for the substitution pathway, which suggests that substitution with retention of configuration can occur in general even though the trigonal bipyramidal species resulting from pseudorotation is significantly unstable and fails to exist as an intermediate.

The complexation of magnesium with hydrogen malonate and formate anions was studied with ab initio calculations. At least HF/6-31G ∗ level of accuracy is necessary for a qualitatively correct description of the complexes. The coordination space of magnesium has to be filled to attain reliable results. If crystal structures are used as experimental references, at least part of the crystal interactions must be properly included in the calculations.

The relative energies of the two minima and the two transition states on the torsional potential of the title compounds were obtained by ab initio molecular orbital calculations with electron correlation energy correction by the Moller-Plesset methods (MP2, MP3 and MP4(SDTQ)), coupled cluster calculations (CCD, ST4CCD, CCSD and CCSD(T)) and configuration interaction energy calculations (CISD, QCISD and QCISD(T)) using the 6-31G ∗ basis set. The calculated trans-gauche energy differences and the rotational barrier heights by the MP2 and CISD methods are slightly different from those with other methods. The calculated relative energies with other electron correlation correction methods are close to each other and close to the experimental values.

The atomic charge distributions of dimethyl ether, ethyl methyl ether, methyl alcohol and ethyl alcohol are obtained by Mulliken and natural population analyses and by electrostatic potential (ESP) fitting methods from HF and MP2 wavefunctions with several basis sets up to the 6-311G (2d,2p) basis set. To evaluate the atomic charge distributions, the dipole moments are calculated from the atomic charge distributions. The dipole moments from the atomic charge distributions, which are obtained by the fitting of the electrostatic potentials, are close to those directly obtained from the wavefunctions. They are also close to the experimental dipole moments, if the wavefunctions are calculated with a polarized basis set and electron correlation correction. The dipole moments obtained by the Mulliken and natural population charges are strongly basis set dependent and do not agree with the experimental dipole moments. The same tendency is observed from the calculations of other ethers and alcohols.

The bonding energies of the parallel and T-shape benzene dimers were calculated using several basis sets including multiple polarization functions. The diffuse polarization functions were important to evaluate the attractive interaction. Small basis sets considerably underestimated the bonding energies. The bonding energies of five orientations of dimers were calculated at the MP2/6-311G(2df, 2p) level. The calculated bonding energy of the displaced parallel dimer was considerably larger than the recently reported value calculated with small basis sets.

The chiral titanium complex-catalyzed ene-type reaction and the Mukaiyama aldol reaction with fluoral are shown to serve as an efficient route to the enantioselective and diastercoselective synthesis of CF 3 -substituted components of biological and synthetic importance.

The nonbonding interaction energies of carbon dioxide dimer were calculated using several basis sets to evaluate the basis set effects. Large basis sets including multiple polarized functions were necessary to evaluate the interaction energies correctly. Small basis sets considerably underestimated the interaction energies. Nonbonding parameters of a model potential of carbon dioxide were refined based on the intermolecular interaction energies of 40 geometrical configurations of dimers calculated by an MP2/6-311+G(2df)-level ab initio method with the basis set superposition error (BSSE) correction. The molar volume and heat of evaporation of liquid carbon dioxide obtained from molecular dynamics simulations with the model potential reproduced the experimental values with an error of only a few percent. On the other hand, the model potential based on the BSSE-uncorrected interaction energies overestimated the attractive interaction and failed to reproduce the experimental values. The structure and lattice...

Relative conformational energies of n -butane, n -pentane and n -hexane were calculated by the DFT method (Becke's exchange and Lee, Yang and Parr's correlation functionals) with the 6-31G ∗ basis set. The calculated energies were compared with experimental values and ab initio calculations. The DFT relative conformational energies agree better with the MP4 energies and experimental values than the HF energies.

The conjugate addition of nitromethane (II), cyclopentadiene (IV) or nitroethanol (VIII) towards α,β,γ,δ-unsaturated aldehydes in the presence of a prolinol-derived organocatalyst proceeds chemoselectively in a 1,4-addition mode.

Diphenylprolinol silyl ether was found to be an effective organocatalyst for promoting the asymmetric, catalytic, intramolecular [6 + 2] cycloaddition reactions of fulvenes substituted at the exocyclic 6-position with a δ-formylalkyl group to afford synthetically useful linear triquinane derivatives in good yields and excellent enantioselectivities. The cis-fused triquinane derivatives were obtained exclusively; the trans-fused isomers were not detected among the reaction products. The intramolecular [6 + 2] cycloaddition occurs between the fulvene functionality (6π) and the enamine double bond (2π) generated from the formyl group in the substrates and the diphenylprolinol silyl ether. The absolute configuration of the reaction products was determined by vibrational circular dichroism. The reaction mechanism was investigated using molecular orbital calculations, B3LYP and MP2 geometry optimizations, and subsequent single-point energy evaluations on model reaction sequences. These calculations revealed the...

The interaction energy potentials for six orientations of the fucose–water complex were calculated for evaluating the magnitude of the CH/O interactions in the complex. The calculations show that the C–H bonds of the nonpolar surface of fucose prefer to have contact with the oxygen atom of the water. The substantial attraction exists between the C–H bonds of fucose and water. The interaction energy calculated for the fucose–water complex at the MP2/aug-cc-pVTZ level is −2.55 kcal/mol. The CH/O interactions in the fucose–water complex are significantly larger than those in the cyclohexane–water complex (−1.13 kcal/mol), which shows that the oxygen atoms of fucose enhance the CH/O interactions. The electrostatic and dispersion interactions are responsible for the attraction in the CH/O interactions in the fucose–water complex, while the electrostatic contributions to the attraction in the CH/O interactions in the cyclohexane–water complex is small. The DFT-SAPT calculations also show that the electrostatic interactions are responsible for the larger attraction in the fucose–water complex. These results suggest that the nature of the CH/O interactions between carbohydrate and water is significantly different from that of the CH/O interactions between saturated hydrocarbon and water.

An excellent linear correlation was found between calculated and experimental total infrared intensities in the region of 500–2000 cm−1 for five partially fluorinated ethyl methyl ethers, HFC-134a, and CFC-11. The calculated results using ab initio molecular orbital method with D95V**(Huzinaga-Dunning’s valence double zeta) show the best linear correlation among basis sets examined in this study. The correlation coefficient with D95V** is 0.9993 although the calculated values are on the average 32% higher than experimental ones.

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 intermolecular interaction potentials of methane, ethane, ethylene and benzene dimers were calculated using several basis sets [up to 6–311G(3d,4p)] with electron correlation correction by the Moller-Plesset perturbation method and basis set superposition error (BSSE) correction. The calculated interaction energies considerably depend on the basis set used. Whereas the interaction energies of the repulsive and Coulombic energy components calculated at the HF level are not affected by the change of the basis set, the dispersion energy component, calculated as the electron correlation energy, greatly depends on the basis set used. A basis set with multiple polarized functions is necessary to calculate the dispersion energy correctly. The use of small basis sets greatly underestimates the dispersion energy.

The intermolecular interaction energies of 132 geometrical configurations of methane dimers were calculated by an MP3/6-311G(3d,3p)-level ab initio method. Nonbonding interaction parameters were fitted using three models (isotropic hydrogen, anisotropic hydrogen, and anisotropic hydrogen with electrostatic interaction) to reproduce the ab initio results. The incorporation of the anisotropy of the nonbonding interaction of hydrogen decreased the RMS error drastically. On the other hand, the incorporation of the electrostatic interaction improved the fitting little. The density, heat of evaporation, and self-diffusion coefficient of liquid methane were calculated by molecular dynamics simulations with the second- and the third-model parameters

Diphenylprolinol silyl ether was found to be an effective organocatalyst for promoting the asymmetric, catalytic, intramolecular [6 + 2] cycloaddition reactions of fulvenes substituted at the exocyclic 6-position with a δ-formylalkyl group to afford synthetically useful linear triquinane derivatives in good yields and excellent enantioselectivities. The cis-fused triquinane derivatives were obtained exclusively; the trans-fused isomers were not detected among the reaction products. The intramolecular [6 + 2] cycloaddition occurs between the fulvene functionality (6π) and the enamine double bond (2π) generated from the formyl group in the substrates and the diphenylprolinol silyl ether. The absolute configuration of the reaction products was determined by vibrational circular dichroism. The reaction mechanism was investigated using molecular orbital calculations, B3LYP and MP2 geometry optimizations, and subsequent single-point energy evaluations on model reaction sequences. These calculations revealed the following: (i) The intermolecular [6 + 2] cycloaddition of a fulvene and an enamine double bond proceeds in a stepwise mechanism via a zwitterionic intermediate. (ii) On the other hand, the intramolecular [6 + 2] cycloaddition leading to the cis-fused triquinane skeleton proceeds in a concerted mechanism via a highly asynchronous transition state. (iii) The fulvene functionality and the enamine double bond adopt the gauche-syn conformation during the C-C bond formation processes in the [6 + 2] cycloaddition. (iv) The energy profiles calculated for the intramolecular reaction explain the observed exclusive formation of the cis-fused triquinane derivatives in the [6 + 2] cycloaddition reactions. The reasons for the enantioselectivity seen in these [6 + 2] cycloaddition reactions are also discussed.

The CH/π contact structures of the fucose-phenol and fucose-indole complexes and the stabilization energies by formation of the complexes (E(form)) were studied by ab initio molecular orbital calculations. The three types of interactions (CH/π and OH/π interactions and OH/O hydrogen bonds) were compared and evaluated in a single molecular system and at the same level of theory. The E(form) calculated for the most stable CH/π contact structure of the fucose-phenol complex at the CCSD(T) level (-4.9 kcal/mol) is close to that for the most stable CH/π contact structure of the fucose-benzene complex (-4.5 kcal/mol). On the other hand the most stable CH/π contact structure of the fucose-indole complex has substantially larger E(form) (-6.5 kcal/mol). The dispersion interaction is the major source of the attraction in the CH/π contact structures of the fucose-phenol and fucose-indole complexes as in the case of the fucose-benzene complex. The electrostatic interactions in the CH/π contact structures are small (less than 1.5 kcal/mol). The nature of the interactions between the nonpolar surface of the carbohydrate and aromatic rings is completely different from that of the conventional hydrogen bonds where the electrostatic interaction is the major source of the attraction. The distributed multipole analysis and DFT-SATP analysis show that the dispersion interactions in the CH/π contact structure of fucose-indole complex are substantially larger than those in the CH/π contact structures of fucose-benzene and fucose-phenol complexes. The large dispersion interactions are responsible for the large E(form) for the fucose-indole complex.

The chiral titanium complex-catalyzed ene-type reaction with fluoral is shown to serve as an efficient route for the asymmetric synthesis of CF 3 -substituted compounds of biological and synthetic importance in extremely high enantiomeric excesses (>95% ee). The ene reactivity of trihaloacetaldehyde including fluoral is estimated in terms of the balance of LUMO energy level vs . electron density on the carbonyl carbon.

The intermolecular interaction potential of the H2-H2 system was calculated by an ab initio molecular orbital method using several basis sets (up to 6-31 lG(3pd)) with inclusion of the electron correlation correction of the Moller-Plesset perturbation method and the basis set superposition error (BSSE) correction of the counterpoise method in order to evaluate the basis set effect. The calculated interaction energies depend strongly on the basis set used. Whereas the interaction energies of the repulsive and coulombic energy components calculated at the Hartree-Fock level are not affected by a change of basis set, the dispersion energy component depends strongly on the basis set used. Parameters of an exp-6-1 type non-bonding interaction potential were optimized on the basis of the MP4(SDTQ)/6-311G(3p) level intermolecular interaction energies of the H2-H2 system.