Taizo Ono

Magnitude and Origin of the Attraction and Directionality of the Halogen Bonds of the Complexes of C6F5X and C6H5X (X=I, Br, Cl and F) with Pyridine

The geometries and interaction energies of complexes of pyridine with C(6)F(5)X, C(6)H(5)X (X = I, Br, Cl, F and H) and R(F)I (R(F) = CF(3), C(2)F(5) and C(3)F(7)) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (E(int)) for the C(6)F(5)X-pyridine (X = I, Br, Cl, F and H) complexes at the basis set limit were estimated to be -5.59, -4.06, -2.78, -0.19 and -4.37 kcal  mol(-1) , respectively, whereas the E(int) values for the C(6)H(5)X-pyridine (X = I, Br, Cl and H) complexes were estimated to be -3.27, -2.17, -1.23 and -1.78 kcal  mol(-1), respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C(6)F(5)X. The values of E(int) estimated for the R(F)I-pyridine (R(F) = CF(3), C(2)F(5) and C(3)F(7)) complexes (-5.14, -5.38 and -5.44 kcal  mol(-1), respectively) are close to that for the C(6)F(5)I-pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short-range (charge-transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C(6)F(5)I- and C(2)F(5)I-pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water-formaldehyde complex. The calculations suggest that the C-I and C-Br halogen bonds play an important role in controlling the structures of molecular assemblies, that the C-Cl bonds play a less important role and that C-F bonds have a negligible impact.

Resolution/Deracemization of Chiral α-Amino Acids Using Resolving Reagents with Flexible Stereogenic Centers

This work has demonstrated that a previously unexplored approach to separation of enantiomers via formation of diastereomeric derivatives with three stereogenic centers has obvious practical potential and deserves further systematic study. The design reported here is based on the unusual application of a configurationally unstable stereogenic nitrogen, which plays a key role in setting up the stereochemical match between the three stereogenic centers in the corresponding products.

Optical Purifications via Self-Disproportionation of Enantiomers by Achiral Chromatography: Case Study of a Series of α-CF3-containing Secondary Alcohols

This work demonstrates that self-disproportionation of enantiomers via achiral chromatography can be recommended as inexpensive and general method for optical purification of enantiomerically enriched compounds. In particular, the advantage of this approach over conventional recrystallization is that it can be used for both crystalline as well as liquid compounds.

DFT‐GIAO calculations of 19F NMR chemical shifts for perfluoro compounds

The 19F NMR shieldings for 53 kinds of perfluoro compounds were calculated by the B3LYP‐GIAO method using the 6‐31G(d), 6‐31+G(d), 6‐31G(d,p), 6‐31++G(d,p), 6‐311G(d,p), 6‐311++G(d,p), 6‐311G(2d,2p), 6‐311++G(2d,2p), 6‐311++G(2df,2p), 6‐311++G(3d,2p), and 6‐311++G(3df,2p) basis sets. The diffuse functions markedly reduce the difference between the calculated and experimental chemical shifts. The calculations using the 6‐31++G(d,p) basis set give the chemical shifts within 10 ppm deviations from experimental values except for the fluorine nuclei attached to an oxygen atom, a four‐ and a six‐coordinated sulfur atom, and FC(CF3)2 attached to a sulfur atom.

Novel source of trifluoromethyl radical as efficient initiator for the polymerization of vinylidene fluoride.

A persistent perfluoroalkyl radical (PPFR), perfluoro-3-ethyl-2,4-dimethyl-3-pentyl, is shown to be a good source of •CF(3) radicals and a useful radical capable of initiating the polymerization of vinylidene fluoride (VDF). NMR characterizations of the resulting PVDF homopolymers showed that polymerization of VDF was exclusively initiated by •CF(3) radicals. The addition of •CF(3) radical onto VDF was regioselective leading to CF(3) -CH(2) -CF(2) -PVDF and the CF(3) end-group acted as an efficient label to assess the molecular weights by (19) F NMR spectroscopy. Various [PPFR](0) /[VDF](0) initial molar ratios lead to CF(3) -PVDF-CF(3) of different molecular weights. When that ratio decreased, both the molecular weights and the thermostability of these PVDFs increased, showing less defects of chaining and higher crystallinity.

Magnitude and Directionality of Halogen Bond of Benzene with C6F5X, C6H5X, and CF3X (X = I, Br, Cl, and F)

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

Noninvasive in vivo electron paramagnetic resonance study to estimate pulmonary reducing ability in mice exposed to NiO or C60 nanoparticles

To develop new methods that can estimate the influences of manufactured nanomaterials on biological systems, the in vivo pulmonary reducing ability of mice that had received inhalation exposures to NiO or C60 nanoparticles was investigated using a 700 MHz electron paramagnetic resonance (EPR) spectrometer.

Novel epoxidation reaction of perfluoroalkenes with trimethylamine N-oxide and iodosylbenzene

Trimethylamine N-oxide and iodosylbenzene were found to be useful reagents for the epoxidation of tri- and tetra-substituted perfluoroalkenes in good to excellent yields. A catalytic epoxidation method was also developed by coupling this reaction with the N-oxidation of trimethylamine by hydrogen peroxide or perbenzoic acid.

Radical copolymerisation of chlorotrifluoroethylene with isobutyl vinyl ether initiated by the persistent perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical

Results of the radical copolymerisation of chlorotrifluoroethylene (CTFE) with isobutyl vinyl ether (iBuVE) initiated by ˙CF3 radicals generated by β-scission of perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical (PPFR) at 90 °C in a batch reactor are reported. 19F NMR spectroscopy enabled the assessment of the molecular weights of the poly(CTFE-alt-iBuVE) copolymer by end-group analysis. It was found that, at low initiator concentrations (≤10 mol%), the ˙CF3 radicals preferably attack the vinyl ether monomer to initiate chain propagation and produce alternating poly(CTFE-alt-iBuVE) copolymers. At initiator ratios of 20 mol%, 19F NMR signals in the CF3 region other than the expected CH2–CF3 are observed and are attributed to ˙CF3 addition patterns due to kinetic effects brought on by monomer solubility. The molecular weights for the copolymer produced from 1%, 5%, and 10% PPFR were found to be 340 000, 237 000 and 122 000 g mol−1, respectively. The copolymer produced from 20% PPFR was oligomeric in nature with a molecular weight of 18 000 g mol−1.

Reactions of highly branched fluoroolefins with methyllithium and methylmagnesium bromide: formations of unexpected polyfluorocyclobutene and polyfluoropentadiene compounds

Introduction of a methyl group into hexafluoropropene trimers was achieved by reactions with organometallic carbon nucleophiles. Unusual cyclization and defluorination occurred simultaneously with a formation of methylated polyfluoroolefins: excess methyllithium provided a polyfluorocyclobutene compound, while a polyfluoropentadiene derivative was formed by use of excess methyllithium.