Tsuneo Hirano

Electronic State and Glow Discharge Decomposition of Tetramethyldisilane

Tetramethyldisilane, a new source gas for amorphous silicon carbide, was decomposed by an rf glow discharge. Its reactivity in the formation of amorphous films was higher than a mixture of monosilane and methane gases. A plasma diagnosis by optical emission spectroscopy was contrastive between the two source gas systems, being consistent with the bond energy of the gases determined by a semi-empirical molecular orbital calculation. Judging from the rf power and the substrate temperature dependences on the optical band gaps of the films, the films prepared from tetramethyldisilane have optical band gaps wider than 2.2 eV and their structures appear to be different from those prepared from a monosilane/methane (1/2) gas mixture under otherwise the same conditions. Carbon and silicon atoms are apparently distributed more homogeneously in the former films than in the latter films.

Organometallic compound with Lewis base—IV : Dimerization of methyl crotonate by aluminum alkyl-tertiary amine complex☆

Abstract Aluminum alkyl-tertiary amine complex was found to induce the catalytic dimerization of methyl crotonate (MCr) to dimethyl 2-methylpent-4-ene-1,3-dicarboxylate ( 1 ) and dimethyl 2-methylpent- cis -3-ene-1,3-dicarboxylate ( 2 ). The of the γ-hydrogen of the MCr molecule. Dimer 2 is formed through the isomerization of dimer 1 . The complex of AlR 3 with a bidentate ligand, sparteine, produces dimer 1 , selectively. The complex of AlR 3 with monodentate ligand NEt 3 , on the other hand, induces the isomerization of dimer 1 to the cis -form of dimer 2 . The coordination number of aluminum alkyl-tertiary amine complex seems to control the dimerization mechanism of MCr.

Anomalous decomposition profile of the excited triplet SiH3F: A prediction by ab initio molecular orbital calculations

In search of new starting materials for producing amorphous silicon by plasma chemical vapor deposition, decomposition profiles through triplet states have been studied for fluorosilanes SiHmF4−m (m=0–4) by energy‐gradient ab initio molecular orbital calculations with the 6–21G** basis set. Anomalous Si–F bond cleavage at the first stage was concluded for triplet SiH3F, while all the other fluorosilanes decompose through the Si–H bond cleavage. The anomaly observed for triplet SiH3F is due to the positive charge on F and to the negative overlap population of the Si–F bond. Thus, SiH3F is expected to be a unique source for amorphous silicon films.

Gas-phase NMR: Part I. Conformational energies of 1,2-disubstituted propanes and a comparison with MM2 and MNDO calculations

Abstract Gas-phase 1 H NMR spectra of 1,2-dichloropropane (1,2-DCP) and 1,2-di(methoxy- d 3 )-propane (1,2-DMP) have been measured. The conformational energies of these molecules in the gas phase were determined from the observed coupling constants under a three rotational isomeric state model and are compared with the theoretical values from MM2 molecular mechanics and MNDO molecular orbital calculations. The results indicate that gas-phase NMR is useful method for the determination of conformational energies of relatively complex molecules, and that the MNDO results are more reasonable than the MM2 results for molecules containing electronegative atoms such as oxygen.

A quantum chemical study on hydrogen radical reactions with methane and silane

A quantum chemical study on the reaction of CH4 , CF4 , SiH4 , and SiF4 with a hydrogen radical is performed on the basis of an ab initio molecular orbital calculation to predict the photochemical reactivity of methane, silane, and their analogues. The transition state geometry of the reactions is determined by employing a 3‐21G basis set. The total energies of reactant molecules at the initial, transition, and final states are calculated by employing a 6‐31G** basis set. The exponential parts of the rate constants of these reactions determined from these energies on the basis of the transition state theory are in good agreement with the experimentally obtained relative rates of the reaction. The present calculation was consistent with the experimental results of photochemical reactions for methane and silane derivatives.

Gas—phase high resolution NMR as a potential tool for conformational studies

Abstract Gas—phase high resolution NMR is a potentially useful new tool for the study of rotational isomerism. The methods of measurement are explained, with the care necessary for sample preparations. The main areas of application at present are a) dynamic NMR study of conformational interconversion processes and b) conformational analysis for populations and energies through coupling constants. For the latter, our recent results on 1,2-disubstituted propanes such as 1,2-dichloropropane, 1,2-di(methoxy- d 3 )propane and 1-methoxy-2-propanol are discussed.

Deuterated Epoxides and Their Polymers. I. Synthesis of cis- and trans-Propylene Oxide-1-d and Their NMR Spectra

Abstract cis- and trans-Propylene oxide-1-d were synthesized from the corresponding propenyl halides via propenyllithium and propylene bromohydrin. Their NMR spectra (about 3% in benzene) were analyzed in terms of ABX3 spin system and the assignment was carried out. The chemical shift of the methylene proton in cis position to the methyl group was found to be Δ = 1.86 ppm and that of the methylene proton in trans position Δ = 2.18 ppm (downfield from HMDS). The H-D couplings were observed in the methine-methylene part spectra decoupled from methyl protons. The observed JHDs agree with the theoretical relation: JHH = 6.5 14 X JHD.

The lowest state of HC2N: potentiality of triangular singlet 1A

Abstract Calculations on the energy of the possible isomers of HC 2 N revealed that the triangular 1 A′ state was lowest lying at 1.3 kcal/mol below the bent 3 A″ state which is theoretically lower than the linear 3 Σ − state. The geometries were determined by the second-order Moller-Plesset (MP2) perturbation method which had been built in the GAUSSIAN 82 program. The geometry of 1 A′ is planar and has the following parameters; R (CC′)=1.418 A, R (CN)=1.432 A, R (NC′)=1.318 A, R (CH)=1.080 A, ∠ NCC′ = 62.98°, and ∠ HCC′ = 137.96°.

Quantum Chemistry of Gauche-Oxygen Effect Observed in Polyethers

Gauche conformation about the central C—C bond in the O—C—C—O bond sequence is sometimes more stable than the trans conformation. This phenomenon is anomalous in conventional stereochemistry in terms of electrostatic interaction between partially negative oxygens and of the bulkiness of the substituents on the C—C bond, but is widely observed in polyethers such as poly (oxyethylene)1) and poly [oxy(l-alkylethylene)]s.2, 3) Abe and Mark called this gauche stabilization a “gauche oxygen” effect and defined its magnitude as the difference between the experimental energy for the gauche conformation relative to that for the trans conformation and the corresponding energy calculated by the molecular force field (MFF) method.1, 4) This definition implies that the gauche-oxygen effect is the least understandable phenomenon within the conventional MFF framework. Thus, a quantum chemical explanation may be desirable.

Gas-phase high-resolution n.m.r. spectroscopy: a potential tool for structural chemistry

A method of gas-phase 1H n.m.r. measurement is outlined and its applications to conformational analysis and intramolecular hydrogen-bond studies are described.