Shigehiro Konaka

Atomic Scattering Factors for Electrons as Calculated by the Partial‐Waves Method

Complex atomic scattering factors were calculated from the partial‐wave scattering theory using the Hartree—Fock atomic potentials for the atoms H to Kr and the Thomas—Fermi—Dirac atomic potential for the atoms Kr to Cm. The partial phase shifts were approximated in terms of modified Bessel functions of the second kind.

Molecular structure of dimethylether as determined by a joint analysis of gas electron diffraction and microwave spectroscopic data

Abstract The molecular structure of gaseous dimethylether has been investigated by a joint analysis of the electron diffraction data and the moments of inertia reported by Blukis et al. The structural parameters were determined to be as follows: r g (CO) = 1.415 ± 0.001 A, r g (CH) av = 1.118 ± 0.002 A, φ av (COC) = 111.8 ± 0.2° φ av (HCH) = 109.2 ± 0.2°, θ(tilt angle of the methyl groups) = 3.6 ± 1.7° and τ(torsional angle of the methyl groups) = 2 ± 11°. The uncertainties represent the limits of error. With the aid of an ab initio geometry optimization, it has been concluded that dimethylether has C 2v symmetry and that each of the methyl groups staggers the opposite C O bond.

Vibrational spectra and conformation of polyethylene glycol complexed with calcium and magnesium chlorides

Abstract Infrared and Raman spectra of polyethylene glycol (PEG) complexed with calcium and magnesium chlorides have been measured in aqueous solutions and in isolated complexes. Composition of the calcium complex was obtained as 4.4±0.1 (CH 2 CH 2 O unit):1 (CaCl 2 ):4.5±0.5 (H 2 O) by elementary analysis. From these results, the conformation of PEG in the calcium complex has been proposed to be an alternate conbination of two conformational sequences, (-TGT-TG′T-GTT-TTG-) and (-TGT-TG′T-TGT-GTT-TTG-). For the magnesium complex, the conformation of PEG is supposed to be similar to that of crystalline PEG, with repetition of TGT for the -CH 2 CH 2 O units. The difference in the structure between the calcium and magnesium complexes was explained by the difference in the cations size.

Molecular structure and conformation of methyl acrylate. A gas electron diffraction study augmented by ab initio calculation and rotational constants

Abstract The molecular structure and conformational properties of methyl acrylate, CH 2 CHCOOCH 3 , were studied by a joint analysis of gas electron diffraction data and rotational constants. The structures optimized by HF/4-31G∗ ab initio calculations taken from the literature were utilized as structural constraints in the data analysis. Mean amplitudes of vibration and shrinkage corrections were calculated on the basis of the vibrational spectra recorded for this analysis. At room temperature the molecule exists in a conformational equilibrium of two forms, s-cis and s-trans, in a ratio of 67(11):33. The following r z structural parameters were found for the s-cis conformer: r( C = C ) = 1.332(7) A ; r( C  C ) = 1.480(6) A ; r( C = O ) = 1.207(2) A ; r( C (= O ) O ) = 1.345(3) A ; r( O  C Me ) − r( C (= O ) O ) = 0.089 A (assumed); r( C  H ) = 1.079(5) A (averaged value); ∠=CC = 120.3(8)°; ∠CC=O = 126.1(5)°; ∠CCO = 110.3(3)°; ∠COC = 116.4(5)°. Parenthesized values are error estimates (3σ) referring to the last significant digit.

Effect of temperature on the infrared band shapes and reorientational and vibrational relaxation of liquid acetonitrile

Abstract Infrared band shapes of the CH stretching ν1 and the CC stretching ν4 vibrations have been measured at various temperatures in the −41–70°C range. The band widths of the fundamental transitions were obtained by resolving the band overlap with hot band transitions and other modes by least-squares fitting with a computer. The reorientational and vibrational relaxation times were obtained by plotting the band widths against the absolute temperature divided by the viscosity. The reorientational relaxation times obtained from the ν1, ν4 and previously studied ν2 band widths are in beautiful agreement with each other and consistent with the previous results by the Raman and NMR methods. To our knowledge, this is the first to obtain the consistent results for the molecular reorientation from different infrared bands without using the Raman results. The vibrational relaxation times for the ν2 and ν4 bands are consistent with the previous Raman results, but, for the ν1 band, the infrared result is at least 20–30% shorter than the Raman results.

Structural and conformational analysis of diethyl ether by molecular orbital constrained electron diffraction combined with microwave spectroscopic data

Abstract The molecular structure and conformation of diethyl ether, C(3)H 3 C(2)H 2 O(1)C(4)H 2 C(5)H 3 , at 27°C was studied by a joint analysis of gas electron diffraction and microwave spectroscopic data. Vibrational mean amplitudes and shrinkage corrections were calculated on the basis of the vibrational spectra measured in the vapor and liquid phases. Ab initio geometry optimization at the HF/4-21G level was performed on four possible conformers and the results were used as structural constraints. Diffraction and vibrational spectroscopic data are consistent with the presence of two conformers, trans-trans (TT, dihedral angles φ 1 (C 4 O 1 C 2 C 3 ) = φ 2 (C 2 O 1 C 4 C 5 ) = 180°) and trans-gauche (TG), in the vapor phase. The compositions of the TT and TG conformers were determined to be 69(8) and 31%, respectively, by the joint analysis. The structural parameters of the TT form determined are r g (OC) = 1.419(1) A, r g (CC) = 1.514(2) A, 〈 r g (CH)〉 = 1.114(2) A, ∠ α COC = 113.5(4)°, ∠ α OCC = 108.6(1)°, ∠ α OCH = 110.4(9)°, and 〈∠ α CCH〉 = 110.5(7)°, where values in parentheses are error estimates (3σ) and those in angle brackets denote average values. The structural differences between the TT and TG conformers were taken from the 4-21G calculations except for the dihedral angles of the TG form, which were determined to be φ 1 = 76(10)° and φ 2 = 161(15)°.

Electron diffraction study of thermal decomposition products of trimethylamine: molecular structure of CH3NCH2

Abstract Structural studies of thermal decomposition products of trimethylamine have been performed by gas electron diffraction aided by mass spectrometry. Trimethylamine vapor is heated in a quartz tube shortly before the nozzle tip which is kept at room temperature. When the temperature inside the quartz tube is 515°C, N(CH 3 ) 3 simply decomposes into CH 4 and short-lived CH 3 NCH 2 . However, more complicated reactions, which include CH 3 NCH 2 → CH 4 + HCN, take place at the reaction temperature of 535°C. The zero-point average structure of N -methylmethyleneimine (CH 3 NCH 2 ) has been determined by a joint analysis of electron diffraction data and rotational constants, and then compared with ab initio calculations. Principal structural parameters are as follows: r z ( N  C ) = 1.279(6) A , r z ( N  C ) = 1.458(8) A and θ z (CNC) = 116.62(12)°. The molecular structure of trimethylamine has been determined much more precisely than that given in the literature.

Molecular structures of tert-butyl alcohol and tert-butyl methyl ether as studied by gas electron diffraction combined with vibrational spectroscopy

Abstract The molecular of tert-butyl alcohol (TBA) and tert-butyl methyl ether (TBME) have been determined by gas electron diffraction. Vibrational spectra have been measured for TBME. Normal coordinate analyses have been performed to obtain harmonic force fields and to calculate mean amplitudes and shrinkage corrections. Principal bond lengths ( r g ) and angles ( r α are: r (OH) = 1.016(14) A, r (CO) = 1.446(4) A, r (CC) - 1.529(2) A, ∠COH = 108(3)° and ∠CCC = 110.9(2)° for TBA r (C 2 O) = 1.448(4) A, r (CC) = 1.532(2) A, ∠COC = 118.9(14)° and ∠CCC = 111.1(2)° for TBME. The results have been compared with values from molecular mechanics and SCF MO calculations. The observed geometry for TBA is consistent with the rotational constant reported by Valenzuela. The r g (CO) value of TBA is about 0.02 A larger than that of methanol. The values of r g (C 2 O) and ∠COC of TBME are about 0.03 A and 7° larger than the corresponding values of dimethyl ether and ethyl methyl ether.

Molecular structure of DI-t-butylsulphide as determined by gas electron diffraction

Abstract The molecular structure of di-t-butylsulphide has been investigated by gas electron diffraction. The molecule has C2 symmetry with the following bond lengths (rg) and angles (rα): r(SC)=1.854(5) A, r(CC)=1.539(3) A, r(CH)=1.127(4)A, ∠CSC=113.2(12)°, ∠CCC=109.6(5)°, ∠CCH=111.2(11)°. The torsional displacement of t-butyl groups from the staggered conformation is 12(8)° and the tilt angle of t-butyl groups is 7(2)°. The result is in close agreement with a molecular mechanics calculation. The values of rg(SC) and ∠CSC are greater by about 0.04 A and 14° respectively than the corresponding values for dimethylsulphide and ethylmethylsulphide, reflecting steric hindrance between the t-butyl groups.

Conformational studies by liquid crystal NMR and ab initio calculations: methyl nicotinate and methyl isonicotinate

Abstract Conformational properties of methyl nicotinate and methyl isonicotinate have been studied by liquid crystal 1 H-NMR spectroscopy combined with ab initio calculations. The solvent used is a mixture of 80 mol.% of EBBA and 20 mol.% of MBBA.Ab initio calculations have been performed with 4-21G and MINI-4 basis sets to estimate molecular structures and the potential functions for internal rotation. Some structural parameters and the energy difference between rotational isomers have been refined by using observed dipolar coupling constants. The correlation between internal rotation and reorientational molecular motion has been taken into account according to the theory of Emsley, Luckhurst and Stockley. The parameters of the mean external potential are found to take similar values for methyl nicotinate and methyl isonicotinate. The energy difference of the two stable conformers of methyl nicotinate is in agreement with the analysis neglecting the correlation between the two motions.