Nobuaki Ohta

ESR evidence of a distorted 2Ag electronic structure for the methylcyclohexane radical cation

Abstract The electronic structure of the methylcyclohexane (Me-cC 6 ) radical cation has been investigated by ESR in a perfluoromethylcyclohexane matrix at 4 K. The ESR spectrum of Me-cC 6 + consists of a triplet of doublets with signals at ≈ 74 G (2H) and ≈ 34 G (1H). With the aid of two selectively deuteriated methylcyclohexanes, Me- d 3 -cC 6 and Me-cC 6 -3,3,5,5- d 4 , the triplet and doublet are assigned to two equatorial hydrogens at the 2 and 5 positions, and to one of the methyl hydrogens in the trans position with respect to a certain elongated bond (C 6 C 1 ), respectively. The electronic structure appears to be a distorted A g state which originates from the 2 A g state of the cyclohexane ring.

Structure and reaction of methylcyclohexane radical cation: ESR studies

Abstract The radical cation of methylcyclohexane (Me-cC6) is detected by ESR after γ-irradiation at 77 K of a solid solution of the parent molecules in perfluoromethylcyclohexane (CF3-cC6F11) matrix. The isotropic 1H hyperfine (hf) splittings observed are identified with the help of a selectively deuteriated compound and INDO MO calculations: a1 = 20.1 G (2H), a2 = 42.7 G (2H), and a3 = 48.3 G (2H) for the two gauche protons of the methyl group, the equatorial methylene protons at the C2 and C6 positions, and those at the C3 and C5 positions, respectively, in a chair form with the methyl group at an equatorial position. The unpaired electron in Me-cC6+ occupies an a″ orbital in Cs symmetry. On warming, the radical cation undergoes deprotonation mainly at either the C3 (or C5) or C4 or both.

Structure of radical cations of some methyl-substituted alkanes: ESR and INDO MO studies

Abstract Origins of the H 1s spin densities on the trans CH protons were reinvestigated for the radical cations of some methyl-branched small alkanes based on ESR results and INDO MO calculations. It was concluded that the delocalization of spin densities could not be ignored to explain the large and non-equivalent proton hf couplings of the radical cations. The conformations of 2-methylbutane +• and 3-methylpentane +• trapped in CClF 2 CCl 2 F were found to be different from the previously reported ones.

Selective reduction of acetophenone to 1-phenylethanol in aqueous media

Abstract In the cathodic reduction of acetophenone to 1-phenylethanol and 2,3-diphenyl-2,3-butanediol in aqueous media, the effects of electrolytic conditions such as electrode materials, supporting electrolyte, electrode potential and additives were systematically studied. When the controlled-potential electrolysis of acetophenone was performed at −2.1 V versus SCE on a Pb plate cathode in water containing both sodium sulfate and cationic surfactants such as cetyltrimethylammonium bromide (CTAB), 1-phenylethanol was selectively formed with current efficiencies of 67–94%. The mechanism for the role of cationic surfactants was discussed.

Radical cations of cyclohexanes alkyl-substituted on one carbon : an ESR study of the Jahn-Teller distorted HOMO of cyclohexane

Cation radicals of cyclohexanes alkyl-substituted on one carbon have been stabilized in perfluoromethylcyclohexane and other halocarbon matrices at 4.2 K and studied by means of ESR spectroscopy. It was found that all have an electronic ground state resembling the 2Ag state of the cyclohexane cation, one of the possible states following a Jahn–Teller distortion of the D3d cyclohexane chair structure. The cations can be classified into two groups depending on the substituted alkyl group. To the first group belong the cations with a methyl group or a primary carbon (ethyl, n-propyl or isobutyl group) attached to the ring. The disubstituted cyclohexane cations of 1,1-dimethylcyclohexane and 1-methyl-1-ethylcyclohexane were also found to have a similar structure. The ESR spectra are characterized by a 1:2:1 three-line pattern with the hyperfine. (hf) splitting due to two magnetically equivalent equatorial ring hydrogens. The magnitude of the splitting was found to depend on the size and number of substituents, ranging from 74 G (methylcyclohexane˙+) to 55 G (isobutylcyclohexane˙+). An additional doublet, 17–34 G, due to a hydrogen on the substituent could be detected in certain cases. Such hydrogens are axial with one of the elongated C–C bonds in the ring structure which contains a relatively large fraction of the unpaired electron. It follows that the substituents are located asymmetrically with respect to an ag-like SOMO in the ring. In the second group a secondary or tertiary carbon connects the substituent to the ring, such as an isopropyl or tert-butyl group. The largest hf splittings are ca. 30 G in magnitude, due to certain hydrogens on the substituent which are axial with respect to the cyclohexyl bond. It follows that an ag-like SOMO in the ring here is symmetrically arranged with respect to the position of the substituent. Hyperconjugation is the dominating mechanism for the spin transfer in all cations reported in this study.

A preliminary report on radical yield alternation in even and odd linear alkanes irradiated at 77 K: ESR evidence

Abstract It has been found that the yields of trapped alkyl radicals in linear alkanes irradiated at 77 K exhibit an alternation depending upon whether the carbon number is even or odd. The alternation becomes more prominent in a series of higher alkanes starting from n-C11H24 to n-C19H40, for which the crystal structures as well as the ESR spectral features are known to exhibit a regular alternation. The results suggest that the radiation chemical events are affected by the molecular packing, that is, the crystal structures at the chain end and/or the interchain structures.

A mobility study on highly stacked conducting polymer films

Apparent mobilities of positive charge carriers in a regioregular poly(3-octylthiophene) film at various doping levels are evaluated by an electrochemical technique combining a potential-step chronocoulometry and an in-situ conductivity measurement. The carrier mobility was 5 x 10 -3 cm 2 V -1 s -1 at the lowest doping level of 0.014 %, and it decreased by about one order of magnitude as the doping level increased up to about 2 %. Further electrochemical doping resulted in the dramatic increase of the mobility, reaching 0.5 cm 2 V -1 s -1 at the highest doping level of 23 %.

Electron paramagnetic resonance and INDO-MO studies of 2-methylbutane, 3-methylpentane and 3-methylhexane cations produced in several halocarbon matrices γ-irradiated at 77 K

The EPR results of the selectively deuteriated solute cations 2-methylbutane, 3-methylpentane and 3-methylhexane (2MB+, 3MP+ and 3MHX+) produced in halocarbon matrices (perfluoro-2-methylpentane, CFCl3, CF2ClCFCl2, CF2BrCF2Br and CF2BrCFBrCl) have been studied by means of INDO-MO calculations. The structures of the cations were found to depend on the matrix. The INDO method has shown that the structural changes can be reasonably interpreted on the basis of the structures of 2MB+.

EPR studies of the formation of alkene cations due to ion–molecule reactions in the 77 K radiolysis of pentane and hexane containing additives

Radiolysis of the two systems, pentane containing 3 mol% octane, and hexane containing 3 mol% nonane, has been investigated at 77 K in the presence of 1 mol% alkenes, EPR studies of alk-2- and -3-ene additives show the formation of the corresponding alk-2- and -3-ene radical cations, whereas alk-1-enes with linear C—C chains are observed to give (E)-pent-2-ene radical cations in the pentane systems and (E)-hex-3-ene radical cations in the hexane systems. The effects of the alk-1-ene additives are attributed to the ion–molecule reaction, i.e.. transfer of H2 from the parent n-alkane radical cations to the alk-1-ene additives to form the alkene radical cations of the parent molecules.

Radiation-induced polymerization of 2,3-dimethylbutadiene in thiourea clathrates

Abstract It has been found that addition of 2,3-dimethylbutane (DBA) to thiourea clathrates containing 2,3-dimethylbutadiene (DBE) induces the production of oligomers of DBE. The gas chromatogram of dimers of DBE showed three separate peaks. They are attributed to a linear dimer (2,3,6,7-tetramethyl-2,6-octadiene) and cyclic dimers (1,2,4-trimethyl-4-isopropylcyclohexene-1 and 1,2,4-trimethyl-4-isopropenylcyclohexane-1). Yields of the dimers as functions of contents of DBA and dose of gamma irradiation are examined.