Ichiro Yamaguchi

Microwave spectra of deuterated ethylenes: Dipole moment and rz structure

Abstract The pure rotational spectra of three deuterated ethylenes, CH2CD2, CH2CHD, and cis-CHDCHD, were observed by microwave spectroscopy, and the rotational and centrifugal distortion constants were determined precisely. The dipole moment of CH2CD2 was calculated from the Stark effects to be 0.0091 ± 0.0004 D. From the observed rotational constants the average structure was calculated to be r z (CC) = 1.3391 ± 0.0013 A , r z (CH) = 1.0869 ± 0.0013 A , θz(CCH) = 121.28 ± 0.10°, and r z (CH) - r z (CD) = 0.00137 ± 0.00037 A , where the errors include one standard deviation in the fitting and errors due to an uncertainty (±0.03°) in θz(CCH) - θz(CCD).

Microwave spectrum of catechol (1,2-dihydroxybenzene)

Abstract The microwave spectra of the normal species and three deuterated species of catechol have been observed in the frequency ranges 8–18.6 and 26.5–40 GHz. The inertial defect and the r s coordinates of the hydrogen obtained from the assigned spectra indicate that the conformation of the molecule is planar with intramolecular hydrogen bonding. A measure of the strength of the hydrogen bond is proposed from the difference of inertial defects in OH and OD species; the strength estimated for catechol almost equals that in 2-chlorophenol.

PAM analysis of the microwave spectra of thioacetic acid, CH3COSH and CH3COSD

Abstract The microwave spectra of two isotopic species of thioacetic acid, CH 3 COSH and CH 3 COSD, have been studied. Using the principal axis method (PAM), including terms through n = 6 in the perturbation series and the denominator correction, the spectra were analyzed and 45 lines for CH 3 COSH and 40 lines for CH 3 COSD were assigned. The parameters obtained by the least-squares analysis are A = 9913.29 ± 0.56 MHz, B = 4923.11 ± 0.23 MHz, C = 3354.60 ± 0.24 MHz, θ = 57.080 ± 0.030°, s = 6.2980 ± 0.0012, and I α = 3.198 ± 0.020 amu A 2 for CH 3 COSH, and A = 9662.80 ± 0.78 MHz, B = 4810.74 ± 0.26 MHz, C = 3273.92 ± 0.18 MHz, θ = 55.097 ± 0.024°, s = 5.9742 ± 0.0016, and I α = 3.171 ± 0.020 amu A 2 for CH 3 COSD. The barrier to internal rotation of the methyl group is V 3 = 222.6 ± 1.4 cal/mole for CH 3 COSH and V 3 = 212.9 ± 1.4 cal/mole for CH 3 COSD. The Stark effect measurements of A species transitions for CH 3 COSH led to the dipole moment μ = 1.821 ± 0.013 D with the components μ a = 0.191 ± 0.010 D and μ b = 1.811 ± 0.013 D.

Microwave spectrum and conformation of glycolic acid

Abstract Microwave spectra of glycolic acid (hydroxyacetic acid), CH 2 OHCOOH 2 , and its five isotopic species (D and 15 O substituted) have been observed and analyzed. The rotational constants for the ground states of all the species, the first and second vibrationally excited states of the normal species, and first excited states of the three deuterated species have been obtained. The dipole moments for the ground state of the normal species were found to be μ a = 1.95 D, μ b = 1.02 D, and μ total = 2.20 D. The r s coordinates of hydrogen and oxygen atoms give an unequivocal result for the conformation of this molecule. It is of planar skeleton and five-membered hydrogen-bonded ring type.

Microwave spectrum and structure of disulfur dichloride, S235Cl2

Abstract The microwave spectrum of disulfur dichloride, S 2 35 Cl 2 , has been studied in the frequency range 9–39 GHz. The Q -branch transitions were assigned with the aid of a diagram (similar to the Loomis—Wood diagram) specifically designed for Q -branch assignment. The assignment of some of the R -branch transitions was confirmed by means of the double resonance method. The rotational and centrifugal distortion constants were obtained. The r 0 structure of this molecule was evaluated with the SCl distance fixed to the electron diffraction value. The structure thus obtained agrees well with that deduced in the electron diffraction study.

MICROWAVE SPECTRUM AND MOLECULAR PLANARITY OF ACETOPHENONE

Abstract The microwave spectrum of acetophenone was observed in the frequency region 9–18 GHz. The rotational and centrifugal distortion constants of acetophenone in the ground and first three excited states of torsion around the CCOCH3 bond have been determined. The determined constants for the ground state are A = 3688.040(11) MHz, B = 1215.048(1) MHz, C = 919.919(1) MHz, ΔJK = −0.250(44) kHz, ΔK = 1.95(68) kHz, and δK = 0.440(22) kHz. The residual inertial defect calculated from the inertial defects of the ground and torsional excited states indicates that the structure of acetophenone is skeletal planar.

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 spectra and structure of 1,2-dichlorobenzene-3d and -4d

Abstract The microwave spectra of six monodeuterated 1,2-dichlorobenzenes-3 d and -4 d , each having 1,2- 35 Cl 2 , 1,2- 35 Cl 37 Cl, or 1,2- 37 Cl 35 Cl, in the frequency range 10–40 GHz, have been analyzed. The r 0 -structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r 0 bond lengths (A) and bond angles (degrees) are as follows: r CC = 1.393–1.398; r CH = 1.080–1.083; r CCl = 1.729(15); ∠CCC = 119.5–120.3; ∠C(1)C(2)Cl(2) = 120.9(5); ∠C(2)C(3)H(3) = 118.7(11); and ∠C(3)C(4)H(4) = 119.5(13). The following distortions in the structure are found. The distortion of the benzene ring is of the same extent as in chlorobenzene and rather smaller than in fluorobenzenes. On the other hand, the two CCl bonds bend outwards from each other by about 1° and the ortho -hydrogen H(3) by 0.6° towards the Cl atom, respectively, from the bisector at the ipso -carbon. The ortho -hydrogen is closer to the chlorine atom. The possibility of a “bent bond” in the CCl has been inspected from the nuclear quadrupole coupling constants of chlorine nuclei.

Microwave spectrum,structure and quadrupole coupling constants of o-dichlorobenzene

Abstract The microwave spectrum of two isotopic species of o -dichlorobenzene, C 6 H 4 35 Cl 2 and C 6 H 4 35 Cl 37 Cl, have been studied. The R -branches of the a-type transition lines in the 8–35 GHz region have been assigned for the ground and first three excited vibrational states of the C-Cl out-of-plane bending mode (A 2 ). The small inertia defect obtained indicates that the molecule is planar. The non-bonded ClβCl distance was obtained using the Kraitchman equation, and the structure of the molecule is discussed. The quadrupole coupling constants of the chlorine nucleus were obtained by measurements of the envelope of the hyperfine structure. The results are χ aa = −37.9 ± 1.3 MHz, χ bb = 7.0 ± 0.7 MHz, and χ cc = 30.9 ± 2.0 MHz for 35 Cl.

Microwave spectrum and the structure of benzoyl chloride

Abstract The microwave spectrum of benzoyl chloride was observed in the frequency range 12–18.6 GHz. Rotational constants have been obtained for the ground vibrational state, the first three excited torsional states of the COCl group, and one of the out-of-plane bending states. The residual inertial defect obtained from the ground and the torsional excited states indicates that the equilibrium conformation is planar. Ab initio MO calculations (STO-3G) showed the potential energy curve as a function of the COCl torsional angle to be rather flat around zero degrees.