The microwave spectrum of the unsymmetrical conformation of 1-chloro-2-methyl propane

The microwave spectrum of 1-chloro-2-methyl propane has been recorded and lines assigned to ³⁵Cl and ³⁷Cl species in the unsymmetrical conformation. The rotational and distortion constants in MHz are: C₄H₉³⁵Cl, A = 7527.05, B = 2146.21, C = 1793.59, Δ_JK = 4.15 × 10^?3, δ_j = ?8.0 × 10^?5; C₄H₉³⁷Cl, A = 7524.40. B = 2091.73, C = 1755.54, Δ_JK = 2.5 × 10^?3, δ_j = 2.0 × 10^?4.     

Microwave spectrum of 3-nitrothiophene

The microwave spectrum of 3-nitrothiophene has been studied in the frequency region 26.5–40.0 GHz. The rotational transitions of the ground state and the first six torsionally excited states have been assigned. The ground state rotational constants have been determined to be A_o=4622.61 ± 0.07 MHz, B_o = 1231.751 ± 0.001 MHz and C_o = 973.062 ± 0.001 MHz. The planarity of the molecule has been demonstrated. The first torsional frequency and the barrier to internal rotation of the nitro group have been estimated as 60 cm^?1 and 3.8 kcal/mole, respectively.     

Étude en ondes millimétriques des variétés isotopiques en 13c et 18o de la molécule de trioxane: Structure de la molécule

The rotational spectra of the molecules (¹³CH₂O)(¹²CH₂O)₂ and (CH₂¹⁸O) (CH₂¹⁶O)₂ have been investigated in the region 30–290 GHz. The rotational constants determined are (MHz):A = 5271.106±0.007, B = 5176.405 ±0.007, C = 2904.376±0.34 for the former, andA = 5267.34±0.3, B = 508I.106±0.3, C = 2872.378± 10 for the latter molecule.The parameter C of the parent molecule (CH₂O)₃ has been determined: 2933.95 ±0.34 MHz. With the value A = B = 5273.258 ±0.002 for the parent molecule the following structural parameters were determined: r(C-O) = 1.4205± 0.005 Å, ∠COC = 109.5±0.5°, ∠OCO = 112±0.5°.     

Microwave spectrum and structure of CF3OOCl

The microwave spectrum of chloroperoxytrifluoromethane has been recorded from 12.5 to 40.0 GHz. Only a-type transitions were observed. The R-branch assignments have been made for both the CF₃OO³⁵C1 and CF₃OO³⁷Cl species for the ground vibrational state. The rotational constants are: A=4808± 12, B=1318.55±0.02, C=1278.28±0.02 MHz for the ³⁵CI species, and A=4748±300,B=1285.28±0.96, C=1246.80±0.96 MHz for the ³⁷Cl species. From a diagnostic least-squares adjustment to fit the six rotational constants the following structural parameters were obtained: r(C-0)=1.377±0.03 Å, r(O-O)=1.445± 0.049 Å, r(Cl-O)=1.69±0.04 Å, ∠COO=108.1±4.2°, ∠ClOOC=99.5±2.0°, and ∠tilt = 6.0±0.9° with reasonable assumptions for the three other structural parameters. The relatively large uncertainty in these structural parameters results from the large uncertainty in the A rotational constants. These parameters are compared to the corresponding ones in some other peroxides. The quadrupole coupling constants have been obtained and are discussed.     

Microwave spectrum of dichloroborane (BHCl2)

The microwave spectrum of dichloroborane has been observed and the rotational constants of four isotopic species are determined as follows: A = 46911.09(7), B = 3185.937(10) and C = 2980.425(14) MHz for the normal species, A = 46747.14(8), B = 3099.543(14) and C = 2904.037(14)MHz for BHCl³⁷Cl, A = 49302.05(24), B = 3185.536(32) and C = 2989.368(51) MHz for ¹⁰BHCl₂ and A = 35153.18(9), B = 3186.026(15) and C = 2918.233(11) MHz for BDCl₂. The following complete r_s structure was determined: r_s(BH) = 1.184(2) Å, r_s(BCl) = 1.735(2) Å and ∠ ClBCl = 120.4(2)°. The hyperfine structure due to the two chlorine and one boron nuclei has been analysed.     

Microwave spectrum and structure of equatorial chlorocyclohexane

The microwave rotational spectra of C₆H₁₁³⁵Cl and C₆H₁₁³⁷Cl have been measured. The rotational constants A, B and C and quadrupole coupling constants were determined. Some structural information was obtained.     

The rotational spectrum of the cyclopentadienylallylnickel complex

The rotational spectrum of cyclopentadienylallylnickel, C₃H₅NiC₅H₅, has been studied using a pulsed molecular beam Fourier transform microwave spectrometer. Twelve a-type transitions were analyzed to obtain rotational and centrifugal distortion constants for the parent C₃H₅⁵⁸NiC₅H₅ complex. The measured rotational constant A = 3107.603(93) MHz is about 160.0 MHz larger than the predicted DFT value, providing evidence for possible fluxional motion in the complex. The large distortion constants, on the order of 100 kHz, provide further evidence for fluxional motion. The experimental constants B = 1302.38(22) and C = 1276.40(15) MHz are in good agreement with the DFT calculated values and confirm the η³-bonding of the allyl ligand to the Ni–C₅H₅ moiety. DFT calculations provide a V₅ barrier for internal rotation about the Ni–C₅H₅ axis of 53 cm⁻¹, with the lowest energy conformation having the central allyl c-atom eclipsed with respect to two C₅H₅ carbon atoms. Several additional rotational lines, possibly those of an exited torsional state, were observed but not assigned.     

Microwave spectra and stable conformations of exo- and endo-norborneols

The microwave spectra of exo- and endo-norborneols and their isotopic species deuterated in the hydroxyl group have been investigated over the frequency range 8–40 GHz. Conventional Stark spectroscopy and microwave—microwave double resonance were used to assign Q and R-branch rotational transitions. From the measured transition frequencies the rotational constants A = 3605.9374(9) MHz, B = 1935.4207(8) MHz and C = 1752.3947(8) MHz have been fitted for exo-norborneol and A = 3151.4865(15) MHz, B = 2095.2483(24) MHz and C = 1914.7057(25) MHz for endo-norborneol. Quantitative measurements of the Stark splittings of selected transitions yielded the dipole components μ_a = 0.53(9) D, μ_b = 1.22(6) D and μ_c = 0.294(4) D and the total dipole moment μ = 1.36(9) D of exo-norborneol. The spectroscopic constants of the deuterated species -were used to deduce the orientation of the hydroxyl group of the only conformer found for each isomer of norborneol.     

The microwave spectrum of 2, 5-dihydropyrrole

The microwave spectrum of 2, 5-dihydropyrrole has been measured up to J = 25 in both the ground and first vibrational excited states. The rotational constants for ν = 0 are A = 7650.61 ± 0.04 MHz, B = 7597.38 ± 0.04 MHz, C = 4085.63 ± 0.04 MHz and for ν = 1 the constants are A = 7650.65 ± 0.04 MHz, B = 7597.12 ± 0.04 MHz and C = 4085.71 ± 0.04 MHz. Centrifugal distortion corrections are included.     

Microwave spectrum of N2D4, 14N quadrupole coupling constants,and the barrier to inversion of the amino group

The microwave spectrum of N₂D₄ has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the ¹⁴N nuclei are X_aa = 4.23 ± 0.04 MHz, X_bb = 1.98 ± 0.05 MHz, and X_cc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N₂D₄ and N₂H₄ the barrier to inversion of a single amino group is computed to be 5.00 kcal mol^?1.     

Microwave spectrum, centrifugal distortion, dipole moment and conformation of 2-methyl-1,3-dioxane

Microwave spectrum of 2-methyl-1,3-dioxane has been investigated in the frequency range 8–40 GHz. Rotational a-type and c-type transitions with J≤40 have been identified. Rotational constants A = 4658.122(2) MHz, B = 2503.221(1) MHz, C = 1783.950(1) MHz and centrifugal distortion constants for the ground vibrational state have been found. Dipole moment components μ_a = 1.43 ± 0.01 D, μ_c = 1.15±0.01 D and overall dipole moment μ = 1.84±0.02 D have been determined. The data obtained are in accord with the chair conformation of the molecule having equatorial arrangement of the methyl group. Original Russian Text Copyright ? 2006 by A. Kh. Mamleev, R. V. Galeev, L. N. Gunderova, M. G. Faizullin, and A. A. Shapkin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No.2, pp. 373–375, March–April, 2006.     

Microwave spectrum of aminoborane,BH2NH2

The unstable species aminoborane, BH₂NH₂, has been identified as a reaction product of ammonia with diborane by microwave spectroscopy. The rotational constants determined are A = 138212 ± 4 MHz, B = 27487.83 ± 0.10 MHz and C = 22878.44 ± 0.11 MHz for ¹¹BH₂NH₂ and A = 138199 ± 6 MHz, B = 28420.36 ± 0.11 MHz and C = 23520.78 ± 0.12 MHz for ¹⁰BH₂NH₂. The dipole moment is 1.844 ± 0.015 D.     

Microwave spectrum,dipole moment and barrier to internal rotation of trans-methyl glyoxal

The microwave spectrum of the trans conformer of methyl glyoxal has been investigated in the frequency range from 8 to 40 GHz. The rotational constants have been determined for the A state: A = 9102.4332(31), B = 4439.8832(27) and C = 3038.9404(22) MHz. Quantitative measurements of the Stark effect have yielded the components of the electric dipole moment: μ_a = 0.1597(11), μ_b = 0.9620(7) and μ_total = 0.9751(7) D. From the splittings of rotational transitions the three-fold barrier to internal rotation of the methyl top has been found to be V₃ = 269.1 (3) cm^?1.     

Microwave spectrum of the s-trans form of 3-pyridinecarbaldehyde

The microwave spectra of the ground state and one excited state of the ON s-trans form of 3-pyridinecarbaldehyde have been measured and assigned. The ground state rotational constants and dipole moment components are: A = 5417.8, B = 1583.289, C = 1225.389 (in MHz) and ¦μ_a¦ = 1.35, ¦μ_b¦ = 0.5 (in debye). The excited state most probably belongs to the C₃C torsion, for which the vibrational frequency is estimated to be 135 ± 30 cm^?1.     

The high resolution rotational spectrum of methyl chloride. The spin—rotation and nuclear magnetic shielding tensors

A high resolution study of the rotational spectrum of CH₃³⁵Cl in the vibrational ground state has been performed using a molecular beam spectrometer. By fitting the measured transitions to an appropriate molecular hamiltonian the values of the following molecular parameters have been obtained: B = 13 292.8763 MHz; D_J = 18.089 kHz; D_JK = 198.76 kHz; H_KJ = 9 Hz; eqQ = ?74.750 MHz; C_⊥ = ?2.7 kHz and C_∥ = ?7 kHz. These data are used to determine the paramagnetic contribution to the chlorine nuclear magnetic shielding tensor. The diamagnetic contribution is also calculated using a semi-empirical method. Comparisons of the average shieldings are made for related molecules.     

Microwave spectrum of C-cyanomethanimine: HCN dimer

The microwave spectra of cis and trans C-cyanomethanimune produced by pyrolysis of dimethylcyanamide were observed. The spectra were assigned with the aid of MO calculations. The rotational constants determined are A = 62550(495), B = 4972.05(8), and C = 4600.33(7) MHz for the cis conformer and A = 54274(366), B = 5073.87(15), and C = 4632.46(13) MHz for the trans conformer.     

Microwave spectrum of cyclohexanone

The rotational spectrum of cyclohexanone has been observed within the frequency region from 18.0 to 40.0 GHz. Transitions in the ground state and six excited states have been assigned. The ground state rotational constants are (in MHz) A = 4195.316 +- 0.059, B = 2502.627 ± 0.005 and C = 1754.443 ± 0.005.From information obtained from relative intensity measurements, these excited states are estimated to be ~ 100 cm^?1 above the ground state for the first excited state of the ring-bending mode and ~ 180 cm^?1 for the first excited state of the ring-twisting mode.     

Microwave spectrum of cyclohexanecarbonitrile

The microwave rotational spectrum of cyclohexanecarbonitrile was investigated in the frequency region 8–40 GHz. From the measured transition frequencies the rotational constants of the two molecular were derived (equatorial isomer: A = 4238.77, B = 1399.172, C = 1128.845 MHz; axial isomer: A = 3005.58, B = 1763.483, C = 1558.615 MHz). Assuming the values of 1.531, 1.096 and 1.159 Å, respectively, for the CC, CH and CN distances, and supposing that the ring structure has the same symmetry as in cyclohexane, the following structural parameters were also obtained: equatorial isomer CCC (carbon ring) = 111.40°, r(CCN) = 1.489 Å, HCCN = 107.42°; axial isomer CCC (carbon ring) = 111.65°, r(CCN) = 1.489 Å, HCCN = 105.53°.     

Angular dependence of the β-proton hyperfine coupling constant in β-substituted ethyl radicals

The β-proton hyperfine coupling constants in β-substituted ethyl radicals Ḣ₂-CH₂-X (X = CH₃, NH₂, OH, F, SiH₃, PH₂, SH, Cl) were computed as a function of the rotational angle α about the C_αC_β bond by ab initio calculations at the UHF/DZ + d level. They follow the relation a_H⨿(θ,α) = A + Bcos²θ + C cosθcosα, where A and B are not significantly affected by the substituent, and C is closely related to the electronegativity of the heteroatom.     

The microwave spectrum of argon-phosphorus trifluoride

The argon-PF₃ complex has been prepared in a supersonic expansion of Ar (98%) and PF₃ (2%). A Fourier-transform micro-wave spectrometer employing a Fabry-Pérot cavity was used to assign 28 rotational transitions. The rotational constants (MHz) and distortion constants (kHz) were A = 7332.468(10), B = 1023.055(2), C = 952.564(2), D_J = 3.53(1), D_JK = 60.4(1) and d₁ = −0.240(7). The argon atom is 3.953 Å (r_c.m.) from the PF₃ center of mass and r_c.m. makes an angle of 70.3° with the C₃ axis of the PF₃.