Takeshi Sakaizumi

Molecular structure of gaseous acetoxime determined by electron diffraction

Abstract The molecular structure of gaseous acetoxime has been determined from a least-squares analysis of electron diffraction data. The skeleton of the gaseous molecule is planar and there are asymmetrical distortions on the CC distances and the CCN angles. The conformations of the two methyl groups are also different. The geometrical molecular parameters obtained are r g ( C 1  C 2 ) = 1.490(3) A , r g ( C 2  C 3 ) = 1.521(5) A , r g ( C 2  N ) = 1.289(1) A , r g ( NO ) = 1.423(2) A , ∠C1C2N = 116.4(2)°, ∠C1C2N = 123.4(3)° and ∠C2NO = 111.2(2)°.

Molecular structure and internal rotation of (Z)-chloroacetaldehyde oxime by gas-phase electron diffraction

Abstract The molecular structure of gaseous (Z)-chloroacetaldehyde oxime has been determined by gas-phase electron diffraction and molecular structure optimization has been carried out by molecular orbital calculations. The molecular skeleton is planar and the potential barrier height to internal rotation around the C C bond ( V 1 ) was estimated to be 2.7 kcal mol −1 . The geometrical parameters obtained are: r g ( Cl)=1.789±0.001A, r g (C C)=1.513±0.003A, r g (C N)=1.284±0.001A, r g (N O)=1.416±0.001A, ∠CCCl=109.7±0.2°, ∠CCN=124.9±0.3°, ∠CNO=110.6±0.2°.

Microwave spectrum, molecular structure, and ab initio calculation of (E)-chloroacetaldehyde oxime

Abstract The microwave spectra of (E)-35ClCH2CHNOH, (E)-37ClCH2CHNOH, (E)-35ClCH2CHNOD, and (E)-37ClCH2CHNOD have been observed in the frequency range from 26.4 to 40.5 GHz. The rotational and centrifugal distortion constants of the four isotopic species in the ground and excited vibrational states were determined. The values of the ΔI( = Ic − Ia − Ib) obtained for the normal (35Cl and 37Cl) and deuterated (35Cl and 37Cl) species in the ground vibrational state were found to be − 16.350(4), − 16.36(4), − 17.06(4), and − 17.07(6) uA2, respectively. The molecular structure of this molecule was determined to be the anticlinal form ( ф 1 :∠ ClCCN = 121.4° , ф 2 :∠ CNOH = 180.0° ), as shown in Fig. 1(a). It was found that ab initio calculation of MP 2 6-31 G ∗∗ level can be used to predict the most stable rotational conformer of (E)-ClCH2CHNOH. The seven structural parameters of the heavy atom skeleton of this molecule were fitted to the eight rotational constants (B and C) of the four isotopic species. The obtained structural parameters (r0) are almost the same as those (rα) obtained previously by a gas-phase electron diffraction study (K. Iijima, T. Miwa, T. Sakaizumi, O. Ohashi, J. Mol. Struct. 352/353 (1995) 161), within the errors. The r(CN and ∠CCN obtained for (E)-ClCH2CHNOH are slightly shorter and drastically narrower than those of (Z)-ClCH2CHNOH. The trend is consistent with those of CH3CHNOH and CH3CH2CHNOH.

Molecular structure of (E)-chloroacetaldehyde oxime by gas-phase electron diffraction

Abstract The molecular structure of gaseous ( E )-chloroacetaldehyde oxime has been determined from electron diffraction data. The geometrical molecular parameters obtained, with estimated limits of error, are r g ( CCl ) = 1.799 ± 0.002 A , r g ( CC ) = 1.516 ± 0.007 A , r g ( CN ) = 1.287 ± 0.003 A , r g ( NO ) = 1.418 ± 0.005 A , ∠CCCl = 109.6 ± 0.4°, ∠CCN = 116.4 116.4 ± 0.7°, ∠CNO = 110.7 ± 0.5° and the torsional angle ф( NCCCl ) = 123.2 ± 1.4° . A least-squares analysis of the data have given the fraction of the E -isomer in the gas phase to be 66 ± 2% at 43°C.

The generation and microwave spectrum of methyl cyanate, CH3OCN

Abstract Methyl cyanate (CH 3 OCN) and its 15 N isotopic species have been generated by reacting O -methylthiocarbamate or O -methylthiocarbamate- 15 N with mercury oxide and have been detected by microwave spectroscopy. The rotational and centrifugal distortion constants have been obtained for normal and 15 N species in the ground vibrational state. The dipole moments of methyl cyanate were found to be μ a = 4.26(6), μ b = 1.24(40), and μ total = 4.26(46) D. From the r s coordinate of the nitrogen atom, we concluded that the observed reaction product was methyl cyanate.

Microwave spectrum: Barrier to the internal rotation of the methyl group of methyl cyanate and its molecular structure

Abstract The microwave spectra of CH 3 OCN, 13 CH 3 OCN, and CH 3 18 OCN, have been observed in the frequency range 18.0–50.0 GHz. The barrier heights of the internal rotation owing to the methyl group of CH 3 OCN, 13 CH 3 OCN, and CH 3 18 OCN in the ground vibrational state have been determined to the 1140(50) cal mol −1 , 1130(50) cal mol −1 and 1110(50) cal mol −1 (1 cal mol −1 = 4.184 J mol −1 ), respectively. The barrier height of the methyl group of methyl cyanate is smaller than that of methoxyethyne (CH 3 OCCH) by about 300 cal mol −1 , which is an isoelectronic molecule of methyl cyanate. The bond length of r (CH 3 O) of methyl cyanate is longer than that of methoxyethyne by about 0.01 A ( 1 A = 0.1 nm ). The difference of the barrier height between the two molecules may depend on the difference of the bond length of r (CH 3 O). This trend is consistent with that of sulfur compounds of CH 3 SCN and its isoelectronic molecule CH 3 SCCH.

Mass and microwave spectroscopic studies of the pyrolysis of oximes

Abstract The mass and microwave spectra of the pyrolysates of three oxime compounds (XCH 2 CHNOH, XH, CH 3 and Cl) were observed at 900, 800, and 550 °C, respectively. The pyrolysates of CH 3 CHNOH and CH 3 CH 2 CHNOH were identified by microwave and mass spectroscopy to be acetonitrile and propionitrile. The pyrolysates of ClCH 2 CHNOH were identified as trans -nitrosoethylene, formaldehyde, and hydrogen cyanide by the same methods. We concluded that trans -nitrosoethylene is produced by dehydrochlorination of the Cl atom and the hydrogen atom of the OH group, and that CH 2 O and HCN appear to be generated by cleavage of CC and NO bonds of 4 H -1,2-oxazete.

Microwave spectroscopic and ab initio studies of pyrolysis products of 2-nitrosopropene (syn form) and its pyrolysis mechanism

Abstract The pyrolysis products of CH2C(CH3)NO (syn form) have been determined by microwave spectroscopy. The pyrolysis products of CH2C(CH3)NO (syn form) and its 15N isotopic species were found to be CH2O, CH3CN, and CH3C15N. The produce of formaldehyde and methyl cyanide suggests that the CC and NO double bonds of CH2C(CH3)NO (syn form) were broken. To explain the generation of the two molecules, a four-membered ring molecule (9) as an intermediate, is proposed. The four-membered ring molecule as an intermediate is also supported by ab initio MO calculation. Applying the pyrolysis mechanism obtained for 2-nitrosopropene (syn form) to that of 1,1,2-trichloronitrosoethane, one of its complicated pyrolysis mechanisms was explained. The rotational constants and geometrical parameters of two intermediates, 9 and CH2CClNO (13), were obtained by ab initio MO calculation (MP2/6-31G**) to predict their microwave spectra.

Molecular structure of dichloroacetaldehyde oxime by gas-phase electron diffraction combined with microwave spectroscopy

Abstract The gas-phase structure of dichloroacetaldehyde oxime (Cl 2 CH–CH NOH, DCAO), was determined by gas-phase electron diffraction (GED) combined with microwave (MW) spectroscopic data. The nozzle temperature in the GED experiment was about 53°C. Structural constraints in the GED data analysis were obtained by the ab initio MO calculation of DCAO at the MP2/6-31G(d, p) level of theory. Vibrational amplitudes, shrinkage corrections for the data analysis of GED and vibrational corrections of the experimental rotational constants were calculated from the harmonic force constants given by normal coordinate analysis. The ( E )-isomer with the dihedral angle of φ (ClCCN)=119.7(2)° was the dominant conformer. The MW spectroscopic investigation and the optimized structure in the ab initio calculations were consistent with the present result. The population of the dominant conformer was 80(1)%. The results of the data analysis indicated that there were two other conformers involved, whose conformations and populations were: ( E )-isomer with one chlorine atom on the plane of the molecular skeleton (10(1)%) and ( Z )-isomer with φ of about 105° (10(1)%). The principal bond distances and angles ( r g /A and ∠ α /deg) of the dominant conformer, ( E )-isomer, were: r (C–C)=1.497(8); r (C N)=1.281(4); r (C–Cl)=1.784(2); r (N–O)=1.415(4); ∠CCN=117.0(8); ∠CCCl=109.4(3); ∠CNO=111.1(5); and ∠NOH=97.2(50). The values in parentheses were three times the standard deviations.

Mass and microwave spectroscopic studies of the pyrolysates and pyrolysis mechanism of 1-chloro-2-isocyanatoethane and 1-chloro-2-isothiocyanatoethane

Abstract The pyrolysates of ClCH 2 CH 2 NCO and ClCH 2 CH 2 NCS were investigated by pyrolysis-mass spectrometry and microwave spectroscopy (Py-MS/MW) at 100–900°C. In the mass spectrum of the pyrolysate of ClCH 2 CH 2 NCO a characteristic ion is seen at m/z 69, while in that of ClCH 2 CH 2 NCS ions at m/z 59, 62, 64, and 85 are observed. The identification by MW revealed that the ion at m/z 69 is the molecular ion of vinyl isocyanate, while the ion at m/z 59 is that of isothiocyanic acid, at m/z 62 and 64 are those of vinyl chloride, and at m/z 85 is that of vinyl isothiocyanate. In spite of the similarity of the two compounds, it was found that the pyrolysis mechanism of ClCH 2 CH 2 NCS was different from that of ClCH 2 CH 2 NCO. The generation of vinyl chloride and isothiocyanic acid from ClCH 2 CH 2 NCS suggests that the CN single bond of ClCH 2 CH 2 NCS may be weaker than that of ClCH 2 CH 2 NCO.