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An algorithm to parallelize the Metropolis sampling was devised and applied to the Monte Carlo simulations using quantum mechanical calculations (QM/MC simulations). As a 4 CPU calculation needs 670 000 s to finish the same QM/MC simulation with the parallelized program, the present algorism reduced the computational time to almost half as long as that of one CPU calculation. The parallelized QM/MC simulation was applied to Diels-Alder reactions between methylvinylketone and cyclopentadiene. The QM/MC (B3LYP/6-311++G∗∗//MP2/6-31G∗,PM3) calculation gave averaged activation energies of 12.7, 13.8 and 15.2 kcal mol−1 in aqueous, methanol and propane solutions. These results are well consistent with those observed.

It is possible to create novel synthetic routes for compounds using synthesis route design systems (SRDS). We have been investigating an in silico screening protocol, which makes it possible to reduce the number of SRDS experiments in developing new synthesis routes. However, there still remains the problem of how to rank synthesis routes for experiments. The experimental yield is considered to be one of the most important factors in determining which synthesis route is better. The present study describes an attempt toward predicting the trends of experimental yields for organic synthesis by fusing computational chemistry and chemoinformatics. We examined whether the prediction of experimental yields for Diels–Alder reactions is feasible using activation energies obtained from Density Functional Theory (DFT) calculations together with the experimental conditions. A partial least squares analysis using these values gave correlation equations for the experimental yields. If it is possible to construct similar correlation equations for other reactions, then SRDS synthetic routes could be ranked on the basis of their predicted yields, and an order can be determined before beginning the experiments.

In this paper we report on the asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides mediated by pybox/ytterbium triflates, -/magnesium bromide, and -/magnesium perchlorate. It was confirmed that the reactions proceed smoothly to give isoxazoline derivatives in high enantiomeric excesses with Mg2+ or Yb3+ complexes and acrylamide dipolarophiles bearing an oxazolidinone or imidazolidinone coordination auxiliary as well as a pybox ligand. In reactions with a dipolarophile bearing 4,4-dimethyloxazolidinone as the coordination auxiliary, an enantiomeric excess (59 % ee) of the corresponding cycloaddition product was achieved by using a slow addition technique to generate nitrile oxides in the presence of Yb(OTf)3/ph-pybox. The cycloaddition reaction of a dipolarophile with an unsubstituted oxazolidinone group in the presence of Yb(OTf)3/ph-pybox at a relatively high temperature (35 °C) produced a higher enantiomeric excess. A relatively low temperature (–78 °C) was required to obtain enantiomeric excesses such as 69 and 87 % ee in the reactions of a dipolarophile bearing an imidazolidinone group to afford cycloadducts in the presence of MgBr2/ip-pybox.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The mechanisms underlying the hydrolysis of methyl acetate and acetamide under acidic conditions were investigated using the MP2/6-311+G(d,p)//MP2/6-31+G(d,p) level of theory. It was necessary to include two water molecules as reactants to obtain a tetrahedral (TD) intermediate for the A AC 2 mechanism that Ingold classified for the hydrolysis of methyl acetate. This mechanism includes two TS structures, one for the formation of the TD intermediate and the other for its decomposition. Since the activation energies were calculated to be 15.7 and 18.3 kcal mol −1 , the second step determines the rate of hydrolysis. The calculated value was close to that observed at ∼16 kcal mol −1 . It was confirmed that the A AC 2 mechanism had a barrier lower by 9.9 kcal mol −1 than the A AL 2 mechanism. The A AC 2 mechanism is also applicable to the acid-catalyzed hydrolysis of acetamide. It is not the TD intermediate with which the NH 3 + moiety forms, but one further step is required to produce the final products, acetic acid and ammonium ion.

Molecular geometries of crown ether derivatives play an important role in capturing and transporting alkali metal ions such as Li + and Na + . As selectivity of the ions is observed in solution, it is necessary to know their molecular structures in solutions. Recently, we investigated stable conformations of 12-crown-O 3 N and its alkali ion complexes in aqueous and acetonitrile solutions. In the present study, we applied a procedure similar to that in previous papers to investigate the side arm effect of 12-crown-O 3 N with an amine arm for capturing Li + and Na + in the two solutions. It was confirmed that the stable structures of Li + and Na + complexes in solutions, especially the geometry of the amine side arm, are highly solvent-dependent. This conformational difference is the key to understanding the high Li + selectivity of 12-crown-O 3 N derivatives with an amine side arm in acetonitrile.

Molecular geometries of crown ether derivatives play an important role in capturing and transporting alkali metal ions such as Li+ and Na+. As the selectivity of ions is observed in solutions, it is necessary to know their molecular structures in solutions. Recently, we investigated stable conformations of 12-crown-O3N and its Li+ complex in aqueous solution by the combination of three programs, the CONFLEX, Gaussian 98, and BOSS programs. In the present study, we applied the same procedure to investigate stable structures of 12-crown-O3N complexes with an alkali ion in aqueous and acetonitrile solutions. It was confirmed that the stable structures of Li+ and Na+ complexes in solutions are highly dependent on the polarity of the solvents.

The photoassisted catalytic degradation of chloroethylene was studied in a tubular photoreactor packed with TiO2 pellets prepared by a sol−gel method. The experiments were performed in a noncirculating mode. Kinetic data and the reaction products were compared with those for the photodegradation of ethylene, trichloroethylene, and tetrachloroethylene. The theoretical calculations at the MP4/6-31G**//B3LYP/6-31G** level indicated that the addition of OH radicals to chlorinated ethylenes is more exothermic than that of Cl radicals by 14.6−29.5 kcal mol-1. Examination of Cl mass balance indicated that the concentration of Cl- collected from the TiO2 surface was higher than that from the product gas stream. When the photodegradation of ethylene was performed on the TiO2 pellets which had been used for that of TCE or which were pretreated with HCl, the formation of chloroacetaldehyde was confirmed by the GC/MS. We proposed that during the photodegradation of the chlorinated ethylenes, the Cl-, as one of the re...

It is possible to synthesize poly(N-substituted maleimide) by using a chiral complex consisting of a zinc and N -diphenylmethyl-1-benzyl-2-pyrrolidinoethanamine (DPhBP). The optical specific rotations [ α ] 435 25 in obtained polymers depend on the chirality of ligands in the catalysts. In the present study, density functional theory (DFT) calculations were adopted to investigate the polymerization mechanism in detail. The bulky diphenylmethyl group in the chiral ligand is effective to enhance the formation of the product in the initiation reaction. The geometry related to the pyrrolidine ring of the chiral ligand in the Zn catalyst is responsible for determining the configuration of polymers. It was also confirmed that the bulky substituent on the N atom of the N-substituted maleimide is another factor for obtaining polymers with high [ α ] 435 25 .

An exploratory study has been carried out on new poly(aminoxyl) radicals as potential bridging ligands for 2p/3d-hybrid-spin metal complexes having network structures. Temperature dependence of the magnetic susceptibility data on the title amine N in the range 2–300 K was analyzed to show that its ground state was a doublet with a quartet state lying 559 K (=1.11 kcal mol−1) above the doublet. B3LYP/6-31G*//B3LYP/6-31G computations on a simplified model molecule (N′) confirmed the doublet ground state by 0.84 kcal mol−1. The methyl compound (C) is a triplet diradical with a singlet state lying 410 K above the triplet. The hexamethyl derivative (B′) of the title borane B has a doublet ground state with an energy gap to a quartet state by 9.9 K. The electronic structures are described qualitatively by p-(N-oxyl-tert-butylamino)phenyl homologues of (·H2C)3X in which X=N,C·, and B atoms, and carries two, one, and no π-electrons, respectively. N and B′ showed two reversible redox waves. MnII(hfac)2 and C gave a black–violet crystalline complex in which the 3d and 2p spins ordered at 60 K.

Ab initio molecular orbital calculations at the MP4(SDTQ)/6-31G∗//RHF/6-31G∗ level of theory were used to obtain detailed insight into the reaction profile on the Mg controlled 1,3-cycloaddition of nitriles oxide with allylic alcohols. It was confirmed that the complex formation reduces the HOMO–LUMO energy gaps of the two reactants. The propensity correlates well to calculated activation energies of the cycloaddition. The syn-stereoselectivity depends on the steric repulsion between the vinyl fragment and the substituent at the α-position of the alcohol or alkoxide. THF or Et2O in the reaction mixture prevent the coordination of R1CNO from forming the Mg intermediate and result in deccelerating the cycloaddition. The results obtained in the present study well explain an important role of the Mg2+ ion in the 1,3-dipolar cycloadditions of nitrile oxides with allylic alcohols.

N,N,N-Tris[p-(N-oxyl-tert-butylamino)phenyl]amine (N) was obtained as dark violet plates by lithiation of tris(4-bromophenyl)amine, followed by reaction with 2-methyl-2-nitrosopropane and oxidation of the resulting tris(hydroxyamine) with Ag2O. An X-ray crystal and molecular structure analysis of the monoclinic single crystal with space group Cc showed that it has neither C3 symmetry nor zwitterionic quinonoid structure. An EPR spectrum in MTHF solution at room temperature consisted of seven lines (aN = 4.06 G (3N) at g = 2.0058). The temperature dependence of the magnetic susceptibility data on N in the range 2−300 K was analyzed in terms of a triangular coupling model for three S = 1/2 spins to give a set of best-fit parameters which placed a doublet state as the ground state with a quartet state lying 559 K (= 1.11 kcal mol-1) above it. B3LYP/6-31G*//B3LYP/6-31G computations were performed on both spin states of a model molecule (N‘) in which all three N-tert-butyl groups in N were replaced with N-meth...

Photosolvolysis of 2-chloropropylbenzene in trifluoroethanol (TFE) produces propylbenzene, indane, 2-trifluoroethoxypropylbenzene and other solvolysis products. Propylbenzene clearly comes from 2-propylphenyl radical intermediate while the other products suggest existence of 2-propylphenyl cation as an intermediate. Density functional theory (DFT) calculations at the B3LYP/6-31G∗∗ level of theory were carried out to research reaction paths for the solvolysis products through the cationic intermediate. Three paths investigated in the present study well explain the products obtained in our experiments. The DFT calculations strongly suggest existence of the phenyl cation as an intermediate in the photosolvolysis of 2-chloropropylbenzene in TFE.

A variety of armed cyclens were prepared in which ester, amide, nitrile, and pyridine moieties were attached as cation-ligating side arms to a 12-membered ring. Ester-, amide-, and pyridine-armed cyclens nicely accommodated a Na(+) ion in a three-dimensional fashion and clearly discriminated the cation from Li(+) and K(+) ions. They extracted Na(+) ion more efficiently and selectively than common Na(+) ion-selective ligands. X-ray diffraction, FAB-MS, (23)Na NMR binding studies, and computer modeling experiments demonstrated that the cyclens having ester-, amide-, and pyridine-functionalized side arms formed highly selective encapsulated Na(+) complexes via a cooperative action of parent cyclen and side arms.

The hydrolysis of esters and amides accompanies a fast reaction, which results in exchange of carbonyl 18O to 16O coming from solvent water. The present study considered two paths as the oxygen exchange mechanism. One, Path 1 called the direct path, is the mechanism that a proton of the OH fragment directly moves from the OH to the 18O fragment in the tetrahedral intermediate. The other, Path 2 called the water-assisted mechanism, is that one water molecule assists transferring a proton to make an 18OH fragment. The MP2/6-31+G* level of theory estimated rather high ΔEgas‡(TD) for the direct path of methylacetate and N-methylacetamide (21.8 and 19.7 kcal mol−1, respectively). The ΔEgas‡(H2O), the activation barrier for the water-assisted mechanism, is very low both for the ester (3.8 kcal mol−1) and for the amide (2.8 kcal mol−1). The ΔG‡(H2O) and ΔG‡(OH), calculated activation free energies including solvent effect, are small in comparison with those observed for the breakdown of TD intermediates to exchange or hydrolysis products. The present MO calculation suggests that one solvent water acts as one of the reactants and facilitates both proton transfer from the OH fragment and proton acceptance from the water to form the new 18OH fragment. It is likely that the oxygen exchange reaction accompanying hydrolysis of esters and amides proceeds via the water-assisted mechanism.

Density functional calculations at the B3LYP/6-311G**//B3LYP/6-311G level of theory were used to study the initial process of ethylene degradation on the TiO2 photocatalyst by adopting the dimeric titanium structure Ti2O6H4 as a model of the catalyst surface. Adsorption energies of water and ethylene were calculated to be 31.9 and 20.4 kcal mol−1. The photogenerated OH radical does not desorb from the catalyst surface and the further reaction with ethylene proceeds since the adsorption energy was estimated to be 39.3 kcal mol−1. Our calculation also indicated that under steady illumination, ethylene directly attacks the OH radical bound to the TiO2 surface even though the surface has vacant sites available for ethylene adsorption.

In the presence of magnesium perchlorate, 1,3-dipolar cycloaddition reactions of nitrile oxides to crotonamide bearing 4-benzyl-5,5-dimethyl-1,3-oxazolidin-2-one as the chiral auxiliary proceeded with a regio- and diastereo-selective manner to afford the corresponding chiral 2-isoxazoline. The mechanisms underlying the diastereoface selection in the cycloaddition reaction were investigated using the B3LYP/6-31G* level of theory.

Ab initio molecular orbital (MO) study on the inversion process of six trimethylene bridges between two degenerate C 6h conformers of [3 6 ](1,2,3,4,5,6)cyclophane suggests that the inversion occurs in a stepwise manner rather than a synchronous mechanism.

The exchange interaction between two triplet carbene centers through diphenyl sulfide 4,4‘-diyl, its sulfoxide and sulfone analogs, and thiaxanthene 2,7-diyl coupling units was studied. These dicarbenes were generated by photolysis of the corresponding bisdiazo precursors in MTHF matrices at cryogenic temperatures. From the temperature dependence of the ESR signals it was found that the dicarbene jointed through the sulfide group has a quintet ground state; it serves as a ferromagnetic coupler. On the other hand, as the oxidation state or the geometry of the sulfur atom was changed to sulfoxide, sulfone, and thiaxanthene groups, antiferromagnetic interaction was observed between the two diphenylcarbene units. The magnitude of the exchange interaction J/k was determined to be 11, −30, −92, and −21 K for diphenyl sulfide, sulfoxide, sulfone 4,4‘-diyl, and thiaxanthene 2,7-diyl couplers, respectively. In the ESR spectra of sterically unconstrained sulfide and its analogs the isolated triplet signals were rat...

The alkaline hydrolysis of amides, N-methyl acetamide 1, acetanilide 2, and N-acetyl imidazole 3, was investigated by use of ab initio molecular orbital calculations. A detailed analysis was performed for two possible mechanisms, Path 1 and 2. Path 1, similar to ester hydrolysis, releases CH3COOH and RNH whereas Path 2 contains the RNH group that extracts the H atom from the OH fragment in the tetrahedral intermediate. In this mechanism, carboxylate ion and an amine directly form. It was ascertained that Path 2 is a better route to decompose the TD intermediate than Path 1 for 1 and 2 in the gas phase. The stability of the leaving group RNH determines which route, Path 1 or 2, is preferred in the gas phase. The solvent effect was estimated for the two mechanisms by using the SCRF calculations of the IPCM model.

A variety of double armed crown ethers were prepared in which amine, amide, ester, nitrile and pyridine moieties were attached as cation-ligating sidearms to diaza-12-crown-4 ring. FAB-MS and 7Li/13C/23Na NMR binding and liquid membrane transport studies revealed that most of them exhibited Li+ cation selectivity, though corresponding single armed lariat ethers showed Na+ cation selectivity. Among them, amine-armed diaza-12-crown-4 derivative offered the highest Li+ ion-selective ionophoric property. Its transport efficiency and selectivity were particularly superior to those of commercially available Li+ ion-selective ionophores.

The photocatalytic degradation of trichloroethylene and tetrachloroethylene in the gas phase, when porous TiO2 pellets were used, produced such undesirable chlorinated byproducts as chloroform (CHCl3) and carbon tetrachloride (CCl4). The formation of byproducts was reduced by increasing oxygen mole fractions in the feed gas stream and/or using the TiO2 pellets fired at a lower temperature. Theoretical calculations indicate that the Cl-radical-initiated reaction produces these byproducts. On the basis of the experimental and the theoretical results, a method to prevent the formation of the chlorinated byproducts is discussed.

Experimental and theoretical investigations of the anti-selective nucleophilic addition induced by BF 3 to 3-formyl-Δ 2 -isoxazolines are described. Ab initio molecular orbital (MO) calculations show that the 3-formyl-Δ 2 -isoxazoline-BF 3 complex prefers s-trans conformation to s-cis conformation. Nucleophiles attack the stable s-trans conformer from the opposite side of C(4) substituent, giving anti-adducts selectively. The BO bond lengths and the stabilization energies suggest that the features of the complex resemble those of aliphatic aldehyde-BF 3 complexes. Introduction of substituent to allyl tin improves the anti-selectivity from 87/13 to 98/2. These results suggest that the reaction proceeds via anti-periplanar transition state.

The hitherto unknown stereochemistry concerning the formation of 2,3-disubstituted cycloheptanones by the Michael addition reaction was studied. The Michael addition of thiophenol to 3-substituted 2-methylene-cycloheptanones in the presence of triethylamine in THF at ambient temperature produced 3-substituted 2-[(phenylthio)methyl]cycloheptanones with high cis selectivity (>96/4), which was unequivocally established by 1 H NMR and X-rays analyses

Reversal of enantioface selectivity was observed by merely switching the solvent from CH2Cl2 (enantiomer ratio of the adduct = 91:9) to THF (14:86) in the asymmetric Diels-Alder reaction catalyzed by the aluminum complex of a newly prepared chiral methol derivative. Negative nonlinear effect on the relationship between enantiomeric excesses of the reaction product and optical purities of the ligand was observed for the reaction in CH2Cl2 whilst linear relationship for that in THF.

Ab initio molecular orbital calculations at the MP4(SDTQ)/6-31G∗//RHF/6-31G∗ level of theory were used to obtain detailed insight into the reaction profile on the Mg controlled 1,3-cycloaddition of nitriles oxide with allylic alcohols. It was confirmed that the complex formation reduces the HOMO–LUMO energy gaps of the two reactants. The propensity correlates well to calculated activation energies of the cycloaddition. The syn-stereoselectivity depends on the steric repulsion between the vinyl fragment and the substituent at the α-position of the alcohol or alkoxide. THF or Et2O in the reaction mixture prevent the coordination of R1CNO from forming the Mg intermediate and result in deccelerating the cycloaddition. The results obtained in the present study well explain an important role of the Mg2+ ion in the 1,3-dipolar cycloadditions of nitrile oxides with allylic alcohols.

The effects of axial ligands on the ground-state geometries, electronic structures and the characteristic optical properties of iron phthalocyanine and its derivatives, FePc and FePcL(n) (L = pyridine (Py) and cyanide (CN(-)); n = 1, 2), were investigated using the density functional theory (DFT) method. The geometries of FePc with a triplet spin state and of FePc(Py), FePc(Py)(2), FePc(CN(-)) and FePc(CN(-))(2) with singlet spin states were optimized under D(4h), C(2v), D(2h), C(4v), and D(4h) molecular symmetries, respectively. The highest occupied molecular orbitals (HOMOs) of FePc, FePc(Py), FePc(Py)(2), and FePc(CN(-)) are pi-type orbitals, which have no contribution from the p(z) atomic orbitals of all nitrogen atoms, whereas the HOMO of FePc(CN(-))(2) is the 7e(g) orbital, which has contributions from the d(xz) and the d(yz) orbitals of the Fe atom mixing with the pi-orbitals of the axial CN(-) ligands. The time-dependent (TD) DFT method gives many optically allowed excitations for FePc, FePc(Py), FePc(Py)(2), FePc(CN(-)), and FePc(CN(-))(2) in the UV-VIS region. Our calculated bands corresponded well with the experimental results. In FePc(Py)(2), the metal-ligand charge transfer (MLCT) transitions from the metal d to the axial-ligand pi*-type orbitals contributed to the B band region. In FePc(CN(-))(2), the MLCT transitions from the metal d to the Pc-ring pi*-type orbitals contributed mainly to the first B band region, but those from the metal d to the axial-ligand pi*-type orbitals did not appear in the energy regions of the Q and B bands. Thus, the axial ligands caused a spectral change in FePc through orbital mixing.

The 1-(p-anisyl)-2-(triisopropylsilyl)vinyl cation 1 and the 1-(p-anisyl)vinyl cation 2 were generated in solution and characterized by NMR spectroscopy. Ab initio molecular orbital calculations using the 6-31 G basis set were performed for cation 2, the 1-(p-anisyl)-2-methylvinyl cation 3, and the 1-(p-anisyl)-2-silylvinyl cation 4, serving as a model cation for 1, to elucidate the importance of α-π aryl stabilization and β-σ bond stabilization in 1-(p-anisyl)vinyl cations with various β substituents. For comparison, the p-anisylmethyl cation 5 was also calculated

In the presence of magnesium perchlorate, 1,3-dipolar cycloaddition reactions of nitrile oxides to crotonamide bearing 4-benzyl-5,5-dimethyl-1,3-oxazolidin-2-one as the chiral auxiliary proceeded with a regio- and diastereo-selective manner to afford the corresponding chiral 2-isoxazoline. The mechanisms underlying the diastereoface selection in the cycloaddition reaction were investigated using the B3LYP/6-31G* level of theory.

The Michael addition of alkoxide anions to nitro olefins is studied in terms of ab initio and MNDO molecular orbital calculations. We have also done experiments using nitro olefins with the same substituents calculated here. It is proposed that the stereoselectivity of the reaction is due to the endo alkoxy effect, which is structural, and the electronic effect in nitronate anion intermediates. The effect does not exist in intermediates of conjugate addition of simple alkyl group to nitro olefines. The difference depends on whether the atom in the γ-position possesses lone pair orbitals or not. High stereoselectivity was observed in the Michael addition to nitro olefins with the bulky substituents of the α-carbon. This is due to the difficulty in rotating the alkoxy fragment about the Cα-Cβ axis

The reaction of nitro olefins with thiolate anions followed by protonation at −78 o C gives anti-β-nitro sulfides. This procedure can be applied to the anti-selective preparation of β-nitro ethers and β-nitro selenides. The reaction of cyclic nitro olefins with aryl thiol gives cis-β-nitro sulfide in excellent selectivity. The conjugate addition of alkylaluminum reagents to phenylthio β-nitro olefins followed by protonation at −78 o C also results in selective formation of anti-β-nitro sulfides. Theoretical calculations show that the methylthio group on the β-position covers the one side of the nitronate plane effectively to give the anti isomer in a stereoselective way

A recent paper by Lui et al. [Z. Liu, X. Zhang, Y. Zhang, J. Jiang, Spectrochim. Acta A 67 (2007) 1232] reported on the theoretical investigations of the fully optimized geometries and electronic structures of iron (II) phthalocyanine (FePc) with the singlet spin state carried out with the restricted density functional theory (DFT) method, where the B3LYP functional was adopted for the exchange-correlation term; however, the triplet spin state was experimentally reported, and we also obtained the triplet spin state by the unrestricted DFT calculations.

Cholesterol-armed cyclens worked as octadentate receptors for Na+, Ca2+, and Y3+ complexes in which four chiral cholesterol-functionalized sidearms were bundled and asymmetrically twisted above cyclen-metal complex platforms. Since the resulting helical metal complexes included chiral, hydrophobic cholesterol residues and charged, hydrophilic metal sites as well as asymmetric coordination geometries, they exhibited unique amphiphilic properties and provided chiral self-aggregates in aqueous solutions. Light scattering, fluorescence, and TEM characterizations demonstrated that Na+ complex with cholesterol-armed cyclen gave a particularly stable self-aggregate in aqueous solution and offered supramolecular environments effective for sensing and detection of amino acid anions. Various dansylamino acid derivatives (dansyl = 5-(dimethylamino)-1-naphthalenesulfonyl) were nicely accommodated in the helicate aggregates to give highly enhanced fluorescence signals, which could be detected by the naked eye at 10(-7) mol/L level. Their inclusion behaviors were analyzed by a Langmuir-type equation, indicating that enantiomer-selective inclusion occurred. MM/MD calculations and circular dichroism (CD) studies further suggested that cholesterol-armed cyclen helicates have chiral and hydrophobic cavities upon self-aggregation, in which the dansylamino acid anions were specifically accommodated. Since these helicates exhibited nonselective binding abilities in solvent extraction experiments of dansylamino acid anions, uncommon chiral recognition and sensing functions were generated by supramolecular alignments of the chiral metal helicates in the aqueous solutions.

A recirculating system of aqueous trichloroethylene (TCE) solutions through the packed bed reactor with TiO 2 pellets has been developed in order to mineralize TCE without difficulties for filtration and recovery of catalyst. The TiO 2 pellets prepared by sol–gel method have photocatalytic activity similar to commercially available PC-101 and PC-102 in the powder form and to ST-B11 pellets. In batch experiments with TiO 2 powders, Degussa P-25 is the most active photocatalyst, which indicates that specific surface area is not an important factor controlling the photocatalytic activity in aqueous solutions. The degradation rates of TCE in the recirculating system with TiO 2 pellets decreased in the presence of H 2 O 2 , while were remarkably accelerated by adding S 2 O 8 2− . The presence of S 2 O 8 2− ions more than 0.01 mol dm −3 completely suppressed hole-electron recombination and mineralized 50 ppm TCE with the 2 h irradiation. In a reactor without TiO 2 photocatalysts, TCE was photodegraded by SO 4 − radicals which produced by photodissociation of S 2 O 8 2− . The degradation rates increased with increase of the initial S 2 O 8 2− concentration. However, TCE was not mineralized but converted to intermediates which were slowly degraded to Cl − by continuing the irradiation.

The S(N)i mechanism, which was previously proposed for the isomerization of 1-acylaziridines to the oxazolines, was reexamined theoretically by performing molecular orbital (MO) calculations of 1-formylaziridine and its derivatives as model compounds and experimentally by using 1(R)-[alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl]-2(S)-methylaziridine (5). At the MP2/6-31G//RHF/6-31G level, the activation energy was estimated to be 38.9 kcal mol(-1) for the S(N)i mechanism in which N-protonated 1-formylaziridine 8a(NH(+)) isomerizes to the N-protonated oxazoline 9a(NH(+)). Intrinsic reaction coordinate calculations showed that this reaction proceeds with retention of the ring carbon configuration. Methyl substitution in the aziridine ring reduces the activation energy by 10 kcal mol(-1). The ring closure of N-(2-chloroethyl)formamide (10a) to the oxazoline, which is a model reaction of the rate-determining step for the addition-elimination mechanism, was estimated to have an activation energy of 45.4 kcal mol(-1). The results of these MO calculations are consistent with the observation that the isomerization of the acylaziridine 5 to the oxazoline 6 is facilitated in the presence of weak nucleophiles such as with BF(3).OEt(2) while the formation of 6 is very slow in the presence of stronger nucleophiles such as p-toluenesulfonate. Both theoretical and experimental results suggest that the S(N)i mechanism explains well the isomerization of (R,S)-5 to the oxazoline with BF(3).OEt(2) in refluxing benzene.

An octadentate Na+ complex of chiral cholesterol-armed cyclen has a quadruple helicated structure and forms a stable self-aggregate in aqueous solution which offers chirality induction of achiral 5-dimethylaminonaphthalen-1-ylsulfonylglycine anion.

The reaction of nitro olefins with thiolate anions followed by protonation at −78 o C gives anti-β-nitro sulfides. This procedure can be applied to the anti-selective preparation of β-nitro ethers and β-nitro selenides. The reaction of cyclic nitro olefins with aryl thiol gives cis-β-nitro sulfide in excellent selectivity. The conjugate addition of alkylaluminum reagents to phenylthio β-nitro olefins followed by protonation at −78 o C also results in selective formation of anti-β-nitro sulfides. Theoretical calculations show that the methylthio group on the β-position covers the one side of the nitronate plane effectively to give the anti isomer in a stereoselective way

Reversal of enantioface selectivity was observed by merely switching the solvent from CH2Cl2 (enantiomer ratio of the adduct = 91:9) to THF (14:86) in the asymmetric Diels-Alder reaction catalyzed by the aluminum complex of a newly prepared chiral methol derivative. Negative nonlinear effect on the relationship between enantiomeric excesses of the reaction product and optical purities of the ligand was observed for the reaction in CH2Cl2 whilst linear relationship for that in THF.

After the photoirradiation of (biphenyl-4-yl)chlorodiazirine (BCD) in ca. 10 K argon (Ar) matrices, the IR spectrum of (biphenyl-4-yl)chlorocarbene (BCC) was measured because the measured bands were in fair agreement with the bands obtained by vibration analysis. The photolyses of BCD−acetonitrile (MeCN)−Ar tricomponent matrices were also carried out to study the reaction of BCC with MeCN. For [MeCN]/ [BCD] > 10, a spectrum that differed from BCC was obtained after the irradiation. The new bands are stable during the irradiation, during increasing temperature (to 45 K), and during storage. An 2-azonia-1-allenide type nitrile ylide (NY) structure was obtained in an optimization. Because the measured bands are in good agreement with those calculated using the vibration analysis for this NY structure, BCC adducts with MeCN immediately after the degradation of BCD.

Two steps are considered for the alkaline hydrolysis of methyl acetate in the gas phase. The first step is the formation of a tetrahedral intermediate and the second is its decomposition. In the present paper, the mechanism for the second step is discussed by using ab initio molecular orbital calculations. The path releasing acetic acid and methoxide anion is an energetically unfavourable path, as easily expected by their pKa values. The final products, acetate ion and methanol, are more stable than the tetrahedral intermediate. We found a hydrogen-bonded acetate–methanol molecule as the intermediate that was more stable than both the tetrahedral intermediates and the final products. We searched and found the transition state which connected the tetrahedral intermediate with the hydrogen-bonded intermediate. The activation energy of the path through the transition state was calculated to be 8.7 kcal mol–1(MP2/6–31 + G**//RHF/6–31G: 5.8). This mechanism explains well the alkaline hydrolysis of esters in the gas phase.

A new method for partition of interaction energy is proposed. The scheme given here easily connects the calculated stabilization energy with the orbital mixing in analyzing orbital interactions of molecules. The method can reveal the relation between the change of electron distribution and stabilization energy. As an example, orbital interaction energies are estimated for diazocompounds, diazomethane and diazirine.

Etude comparative de la photodissociation du thioformaldehyde et du formaldehyde. Trans-isomerisation du thioformaldehyde. Structure electronique de l'etat de transition. Cinetique

The mechanism of the conversion of vinylazides into 2H-azirines is examined by use of ab initio MO calculations. It is ascertained that vinylnitrenes have very weak bonds between the vinylazides and nitrogen molecule parts. It seems to decompose readily into the two fragments. This is one of the most characteristic features of vinylazides. The reaction is shown to proceed with N2 at the tail of the vinylnitrene part. This mechanism accounts well for experimental results of the reaction.

Electronic structures of different d configurations have been studied in relation to the facility of protonation to dinitrogen ligand in Cr(0) and Co(I) complexes. The d6 Cr complex has much better MO's for protonation than the d8 Co complex. This difference largely affects the protonation energies and the reduction of nitrogen molecule in these complexes.

A study has been made on the mechanism of ester hydrolysis in micellar catalysis, using model systems with ab initio MO calculations. The study ascertained that neutral imidazole cannot form a tetrahedral (TD) intermediate with esters since its basicity is very weak; the present MO calculations indicate that, immediately after its formation, the TD intermediate from p-nitrophenyl acetate and the imidazolyl anion decompose into p-nitrophenol and N-acetylimidazole. This accords with the experimental finding that p-nitrophenol is released quickly so that measuring the UV spectra of p-nitrophenol enables the reaction to be monitored. The TD intermediate formation step governs the enantioselectivity of micellar catalysis. N-Acetylimidazole reacts with the OH anion taken in from the liquid phase. We examined two paths for the decomposition: one similar to that of ester hydrolysis and the other the direct product formation of the acetate anion and imidazole. MP2/6-31+G//RHF/6-31 G level calculations show that, in the activation energy, the latter mechanism is lower than the former by 7.5 kcal mol–1.

The hitherto unknown stereochemistry concerning the formation of 2,3-disubstituted cycloheptanones by the Michael addition reaction was studied. The Michael addition of thiophenol to 3-substituted 2-methylene-cycloheptanones in the presence of triethylamine in THF at ambient temperature produced 3-substituted 2-[(phenylthio)methyl]cycloheptanones with high cis selectivity (>96/4), which was unequivocally established by 1 H NMR and X-rays analyses