Jun Nakagawa

Microwave spectrum, structure, dipole moment, and internal rotation of fluoromethyl methyl ether

Abstract Microwave spectra of fluoromethyl methyl ether and its 10 isotopically substituted species were measured. The r s structure of this molecule was determined from the observed moments of inertia. Structural parameters obtained for this molecule, which was in the gauche form, were compared with those of the analogous molecules. Dipole moments of the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment is 1.744 ± 0.029 D making an angle of 100°54′ with the Oue5f8CH 2 bond toward the Cue5f8F direction and lies in the plane whose dihedral angles with the FCO and COC planes are 114°9′ and 44°56′, respectively. The barrier to internal rotation of the methyl group was calculated taking into account the coupling effect with the skeletal torsion using the observed splitting data of the spectra in the ground, first excited methyl torsional, and skeletal torsional states. The barrier, skeletal torsional frequency, and coupling term were determined to be V 3 = 1538 ± 40 cal/mole, ω t = 158 ± 4 cm −1 , and V s = 490 ± 500 cal/mole, respectively.

Microwave spectrum and internal rotation of 2-butyne-1, 1, 1-d3 (dimethylacetylene), CH3C≡CCD3

The rotational transitions of CH3C≡CCD3 have been observed for J=13←12, 15←14, 18←17, 19←18, 20←19, 22←21, 23←22, and 26←25 using a source‐frequency modulation microwave spectrometer with a 3.7 m long free space absorption cell maintained at −50 to −60u2009°C. The observed spectrum clearly shows the effect of internal rotation with a small potential barrier. The expression for the rotational transition frequency derived by Kirchhoff and Lide [J. Chem. Phys. 43, 2303 (1965)] using a second‐order perturbation theory for the contributions of the internal rotation was employed in analyzing the observed spectrum, and the least‐squares analysis has yielded the rotational constant B=2982.4980±0.0011 MHz and a few centrifugal distortion constants. The barrier height to internal rotation has been estimated to be 5.62±0.16 cm−1.

Microwave spectrum, structure, dipole moment and internal rotation of allylsilane

Abstract Microwave spectra of allylsilane and its 13 C and deuterium substituted species have been measured and assigned for the skew isomer. The r s structure was determined with the aid of several assumptions. Some of the parameters determined are; r (Cue5fbC) = 1.328 ± 0.007 A, r (Cue5f8C) = 1.492 ± 0.008 A, α (CCC) = 126.7 ± 0.8°, α(CCSi) = 111.6 ± 0.5° and τ(CCCSi) = 106.8 ± 1.1°. Dipole moments and their components were also determined for the CH 2 = CHCH 2 SiH 3 and CH 2 =CHCH 2 SiD 3 species. Hyperconjugation between the Cue5fbC π bond and the Cue5f8Si σ bond is discussed.

Internal rotation and molecular structure of ethaneselenol by microwave spectroscopy

Abstract The microwave spectra of ethaneselenol and its deuterated and 13 C-substituted species were measured and assigned for the gauche and trans isomers. The double minimum splittings in the gauche isomers were directly observed for the species having a symmetry plane in the frame part. The rotational constants and the torsional splitting of the gauche isomer of the parent species were determined to be A = 27 148.86 ± 0.05, B = 3 623.68 ± 0.01, C = 3 399.21 ± 0.03, and Δ ν = 1 083.33 ± 0.04 MHz. From the torsional splittings of the parent and SeD species together with the vibrational frequencies already reported by Durig and Bucy, the Fourier coefficients of the selenol internal rotation potential function were determined to be V 1 = −44 ± 17, V 2 = −260 ± 3, V 3 = 1202 ± 16, and V 6 = −43 ± 9 cal/mole. From the rotational constants obtained, the r s structural parameters of the gauche and trans isomers were determined. The structural parameters in the skeletal part for the gauche isomer are r (Cue5f8C) = 1.524 A , r (Cue5f8Se) = 1.957 A , r (Seue5f8H) = 1.467 A , α(CCSe) = 113°31′, α(CSeH) = 93°05′, and the dihedral angle τ(CCSeH) = 61°39′. Those for the trans isomer are r (Cue5f8C) = 1.525 A , r (Cue5f8Se) = 1.962 A , r (Seue5f8H) = 1.440 A , α(CCSe) = 108°43′, and α(CSeH) = 93°30′. These parameters were compared with the corresponding ones of ethanethiol.

Microwave spectrum, structure, dipole moment and internal rotation of isopropyl methyl ether

Abstract Microwave spectra of isopropyl methyl ether and its three deuterated substituted species have been measured and assigned for the isomer with C 1 symmetry. A plausible structure was proposed from the moments of inertia obtained. Two Cue5f8Cue5f8O angles at the gauche and trans positions with respect to the Oue5f8CH 3 group differ by 6° with each other and the isopropyl group inclines to the lone pair electrons on the oxygen atom. The dihedral angle between the Cue5f8Oue5f8C and Oue5f8Cue5f8C planes at the gauche position is 71.9°. The barrier to the internal rotation of the methoxy group is 17 25 cal mol −1 , which is much lower than those of n-alkyl methyl ethers. The direction of the dipole moment nearly coincides with the bisector of the Cue5f8Oue5f8C angle and lies in the Cue5f8Oue5f8C plane.

Microwave spectrum, structure, and dipole moment of the trans-trans isomer of methylpropylether

Abstract Microwave spectra of the trans-trans (TT) isomer of methylpropylether and its 12 isotopically substituted species were measured. The r s structure of this isomer was determined from the observed moments of inertia. Structural parameters of this isomer were roughly equal to those of the reported r s structures of trans -ethylmethylether and propane. Dipole moments of the TT isomer for the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment was μ a = 0.082 ± 0.010, μ b = 1.104 ± 0.013, and μ total = 1.107 ± 0.013 D making angles of 4°17′ with the b -inertial axis, of 6°7′ with the bisector of the COC angle. The barrier to internal rotation of the CH 3 C group was calculated to be 3300 ± 60 cal/mole from A-A splittings of the spectra in the CH 3 C excited torsional state.

Microwave spectrum, structure, dipole moment, and internal rotation of methylpropargylether

Abstract Microwave spectra of methylpropargylether and its nine isotopically substituted species were measured. The plausible structure of this molecule was determined from the observed moments of inertia. The r s structural parameters of the OCH 3 part of the molecule could be obtained and were compared with the corresponding parameters of the analogous molecules. The dipole moment and its direction in the molecule were determined by Stark-effect measurements. The barrier to internal rotation of the methyl group was determined from the A - E splittings of the spectra reported by K. M. Marstokk and H. Mollendal ( J. Mol. Struct. 32, 191–202 (1976) taking into account the coupling effect of the skeletal torsion.

Vibration—rotation spectrum of methyl cyanide— analyses of ν2 and ν3 + ν4 bands

Abstract Infrared spectrum of methyl cyanide was recorded in the region from 2235–2320 cm −1 with a working resolution of 0.05 cm −1 . The transitions of two parallel type bands ν 2 and ν 3 + ν 4 as well as the associated hot bands are assigned. Since the molecular constants for the ground and ν 8 vibrational states are known precisely by microwave study for this molecule, highly accurate molecular constants for the upper vibrational states have been determined from those data by a least-squares procedure.

Internal rotation in propyl mercaptan by microwave spectroscopy

Abstract The microwave spectra of propyl mercaptan and its six deuterated species were assigned for two rotational isomers, the trans-gauche and trans-trans forms, where the first refers to the isomerism around the central Cue5f8C bond, and the second, to the one around Cue5f8S bond. The double minimum splittings of the gauche isomers were directly observed for the species having the symmetry plane in the frame. The rotational constants and the torsional splitting of the gauche isomers of the normal species were determined to be A = 23 907.47 ± 0.09, B = 2345.597 ± 0.006, C = 2250.338 ± 0.009, and Δ ν = 1613.01 ± 0.04 MHz. From the torsional splittings of the normal and SD species and the energy difference of two isomers, the Fourier coefficients of the thiol internal rotation potential function were determined to be V 2 = −353 ± 6, and V 3 = 1310 ± 9 cal/mol on the assumption that V 1 was the same as that of ethyl mercaptan. The dipole moments and their components were also obtained from the Stark effect measurements of the two isomers of the normal and SD species. The directions of the dipole moments were discussed.

Microwave spectrum of methyliodosilane: Determination of the dipole moment and eqQ of an asymmetric top molecule containing an atom with a large nuclear quadrupole moment

Abstract Microwave spectra of methyliodosilane and its deuterated species have been measured. A least-squares analysis for the observed frequencies yielded rotational constants and quadrupole coupling constants of the parent species as: A = 14 747.837 ± 0.054, B = 1893.504 ± 0.003, C = 1728.518 ± 0.003, χ aa = −1012.65 ± 0.43, η a χ aa = χ bb − χ cc = −161.96 ± 0.37, and | χ ab | = 478.29 ± 0.84 (all in MHz). The dipole moment of the parent species was determined from Stark effect measurement of some hyperfine components of the 3 03 -2 02 transition to be μ l = 1.862 ± 0.005, μ a = 1.831 ± 0.005, and μ b = 0.336 ± 0.005 D. Also the product among μ a , μ b , and χ ab was concluded to have a positive sign from the Stark shift observed. A brief discussion has been given on the procedure for determining the dipole moment of a molecule containing an atom with a large nuclear quadrupole coupling moment.