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.     

Electron diffraction study on the molecular structure of methane sulphonyl fluoride

The molecular structure of methane sulphonyl fluoride in the vapour state was studied by electron diffraction. Assuming a value of 2.480A?for the distance between the oxygen atoms from a microwave determination, the following geometrical parameters (r_a structure) have been obtained: r(C-H) = 1.093±0.010Å, r(S-O) = 1.410±0.003Å, r(S-F) = 1.561 ±0.004Å, r(S-C) = 1.759±0.006Å, ∠F-S-C = 98.2±1.5°, ∠-S-F = 106.2±0.4°, ∠-O-S-O = 123.1 ±1.5° and ∠H-C-H = 112.9±1.9°. All the observed variations in the molecular geometries of (CH₃)₂SO₂, CH₃SO₂Cl, CH₃SO₂F and SO₂F₂ may be accounted for by the valence shell electron pair repulsion theory. It is particularly advantageous to combine electron diffraction and microwave data in studying sulphone molecular geometries.     

An electron diffraction study of the molecular geometry of dimethyl sulphone

The present electron diffraction study of dimethyl sulphone eliminates the discrepancy between the values of the parameter ∠O-S-O obtained by microwave spectroscopy and electron diffraction. The following geometrical parameters (r_a values) have been obtained: r(C-H) = 1.114±0.003 Å, r(S-O) = 1.435±0.003 Å, r(S-C) = 1.771±0.004 Å, ∠C-S-C = 102.6±0.9°, ∠O-S-O = 119.7±1.1° and ∠S-C-H = 108.5±0.8°. Comparison of sulphone molecular geometries shows a trend toward longer S-O bonds and smaller O-S-O bond angles as ligand electronegativity decreases. The constancy of the O?O interatomic distance indicates the importance of non-bonded interactions.     

The microwave and infrared spectra and structure of hydrothiophosphoryl difluoride

The microwave spectra of ³²SPHF₂, ³⁴SPHF₂ and ³²SPDF₂ have been analyzed. The structural parameters obtained from this analysis are: d(S-P) = 1.867±0.005Å, d(P-F) = 1.551 ±0.005Å, (P-H) = 1.392±0.005Å, ∠SPF = 117.4 ± 0.2 °, ∠SPH = 119.2±0.2 °, ∠FPF = 98.6±0.2 °. Centrifugal distortion coefficients were obtained for ³²SPHF₂. The spectra of two vibrational excited states of ³²SPHF₂ were observed. The two sets of rotational constants (A) 8336.72, 3726.70, 2807.56 MHz and (B) 8344.88, 3727.73, 2798.75 MHz were associated with the vibrational states with measured infrared frequencies 419 cm^?1 and 344 cm^?1 respectively. An analysis of the infrared spectrum is included. Dipole moment measurements yielded μ = 1.87±0.03 D for ³²SPHF₂ and μ = 1.86±0.03 D for ³²SPDF₂     

An electron diffraction and CNDO/2 investigation of the molecular structure and internal rotation of hexafluorodisilane,Si2F6

The molecular structure and internal rotation of Si₂F₆ were investigated by electron diffraction of gases. The following r⁰_α -values for the geometric parameters were obtained: r(Si-Si) = 2.317 ± 0.006 Å, r(Si-F) = 1.564 ± 0.002 Å and ∠FSiF = 108.6° ± 0.3°. The barrier to internal rotation was found to be between 0.51 ± 0.10 and 0.73 ± 0.14 kcal mol^?1, depending on different assumptions of temperature drop due to gas expansion in the nozzle. Attempts were made to calculate the potential barriers for Si₂X₆ molecules with X as H, F and Cl, using the CNDO/2 approximation. When the 3d orbitais of silicon are taken into account, these results differ widely from the experimental values in the case of Si₂Fg₆ and Si₂Cl₆. Neglecting the 3d orbitais of silicon the theoretical and experi- mental potential barriers agree very well.     

Microwave spectrum and substitutional structure of CH2DF

Forty-two transitions of the microwave spectrum of CH₂DF have been observed in the region between 75 and 450 GHz. The measurement of both a-type and b-type transitions makes possible the analysis of the spectrum and the accurate calculation of the rotational constants (in MHz): = 119 675.0535 ± 0.074, = 24 043.4415 ± 0.072, ? = 22959.3732 °0.072, °j = 0.049371 ±0.00011, °_jk = 0.34268 ±0.0006, 2_k = 3,3774 ± 0.0035, δ _j = 0.002329 ± 0.000045, δ_k = 0.0687 ± 0.036. These constants, in combination with the results of earlier work on the symmetric speci r_s structure calculation based entirely on high-accuracy microwave data. The structural parameters are r_CH = 1.100 Å, r_CF = 1.383 Å, and ∠HCH = 110° 37'.     

The zero point average structure of isobutane as determined by electron diffraction and microwave spectroscopy

The molecular structure of isobutane in the gas phase was investigated by combining electron diffraction data with microwave spectroscopic rotational constants of Lide.The analysis indicated that the tertiary C-H distance (r_g = 1.122±0.006 Å) was substantially longer than the average methyl C-H distance (r_g = 1.113±0.002 Å). Other structural parameters obtained were: r_g(C-C) = 1.535±0.001 Å, ∠CCC = 110.8±0.2°, and the average ∠CCH (methyl) = 111.4±0.2°.     

The molecular structure of selenium oxychloride as studied by electron diffraction

The molecular geometry of selenium oxychloride has been studied by electron diffraction. The internuclear distances (in terms of r_a) are: r(Se-O) 1.612 ± 0.005 Å, r(Se-Cl) 2.204 ± 0.005 Å, r(Cl β O) 3.064 ± 0.012 Å, r(Cl β Cl) 3.295 ± 0.016 Å. The bond angles are ∠Cl-Se-O 105.8 ± 0.7° and ∠ Cl-Se-Cl 96.8 ± 0.7°. The structural parameters of three simple selenium-oxygen compounds are compared with those of their sulphur analogs in terms of the valence shell electron pair repulsion model.     

Molecular structure of carbonyl fluoride as studied by gas electron diffraction and microwave data

The molecular structure of carbonyl fluoride has been determined by electron diffraction. The results have been used in conjunction with the rotational constants reported by Carpenter in a combined structure analysis. The values so obtained are r_z (C=O) = 1.1717 ± 0.0013 Å, r_z (C-F) = 1.3157 ± 0.0005 Å, and ∠_zF-C-F = 107.71 ± 0.08°. These agree with the corresponding parameters estimated by Carpenter from the rotational constants alone. The effective constants, α₃, representing the cubic anharmonicity of bond stretching vibrations have been estimated.     

Nuclear quadrupole coupling constants of thionyl chloride

The nuclear quadrupole structure of some low J transitions with large splittings has been measured for thionyl chloride (SO³⁵Cl₂) and analysed in terms of a first order perturbation. The following nuclear quadrupole coupling constants were obtained: x_aa = ?25.01 ± 0.07 MHz, x_bb = ?0.03 ± 0.45 MHz and x_cc = 25.04 ± 0.45 MHz.     

The structure and conformation of dichloroacetyl chloride as determined by gas-phase electron diffraction

The structure and conformation of dichloroacetyl chloride have been determined by gas-phase electron diffraction at nozzle temperatures of 20 and 119°C. The molecules exist as a mixture of two conformers with the hydrogen and oxygen atoms syn and gauche to each other. The composition (mole fraction of syn form) of the vapor was found to be 0.72 ± 0.06 and 0.73 ± 0.12 at 20 and 119°C, respectively, corresponding to almost equal energy for the two forms. The results for the distance (r_g), angle ∠α and r.m.s. amplitude (l) parameters obtained at the two temperatures are entirely consistent. At 20°C the more important parameters, with estimated uncertainties of 3σ are: r(C-H) = 1.062(0.049)Å, r(C0) = 1.189(0.003)Å, r(C-C) = 1.535(0.008)Å, r(CO-Cl) = 1.752 (0.009)Å, r(CHCl-Cl) = 1.771(0.004)Å, ∠C-CO = 123.3(1.3)°, ∠C-CO-Cl = 113.9 (5.9)°, ∠C-CHCl—Cl = 109.5(1.5)°, ∠C1-C-Cl = 111.7(0.5)°, ∠Cl-C-H = 108.0(1.5), φ₁ (HCCO torsion angle in the syn conformer) = 0.0° (assumed), φ₂ (HCCO torsion angle in the gauche conformer) = 138.2(5.1)°.     

The molecular geometry of the addition compound Cl3Ga.NH3 as studied by electron diffraction

The molecular geometry of the complex of gallium trichloride with ammonia, Cl₃Ga.NH₃, has been studied by electron diffraction. The most important internuclear distances in terms of r_a parameters are as follows: r(Ga-Cl) = 2.142±0.005Å, r(Ga-N) = 2.057±0.011Å, r(Cl?Cl) = 3.642±0.010Åand r(Cl?N) = 3.242±0.012Å. As in the case of the aluminium analogue, the flat pyramidal configuration of the GaCl₃ part of the complex suggests a planar equilibrium structure for free GaCl₃. The distance between the donor and acceptor parts may indicate a somewhat weaker interaction than is the case in the aluminium analogue.     

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°.     

Molecular structure and conformational composition of gaseous 1,1-dichloro-2-bromomethyl-cyclopropane and 1,1-dichloro-2-cyanomethyl-cyclopropane as determined by electron diffraction

The molecular structure of the title compounds have been investigated by gas-phase electron diffraction. Both molecules exist as about equal amounts of the two gauche conformers. There is no evidence for the presence of a syn conformer, but small amounts of this form cannot be excluded. Some of the important distance (r_a) and angle (∠_α) parameters for 1,1-dichloro-2-bromomethyl-cyclopropane are: r(CH) = 1.095(19) Å, r(C₁C₂) = 1.476(11) Å, r(C₂C₃) = 1.517(31) Å, r(CCH₂Br) = 1.543(32) Å, r(CCl) = 1.752(6) Å, r(CBr) = 1.950(13) Å, ∠CCBr = 110.5(1.9)°, ∠ClCCl = 111.9(6)°, ∠CCC = 117.5(1.3)°, σ₁ (CC torsion angle between CBr and the three-membered ring for gauche-1) = 116.2(5.6)°, σ₂ = −132.7(7.6). For 1,1-dichloro-2-cyanomethyl-cyclopropane the parameter values are: r(CH) = 1.101(16) Å, r(C₁C₂) = 1.498(9) Å, r(C₂C₃) = 1.544(21) Å, r(C₂C₄) = 1.497(33) Å, r(CCN) = 1.466(26) Å, r(CN) = 1.165(8) Å, r(CCl) = 1.754(5) Å, ∠CCCN = 113.7(2.0)°, ∠CCC = 122.8(1.6)°, ClCCl = 112.5(4)°, σ₁ = 113(13)°, σ₂ = −124(10)°.     

Molecular structure of 1,1-difluoroethylene as determined by gas phase electron diffraction and microwave data

The structure of 1,1-difluoroethylene was determined, from gas phase electron diffraction data obtained independently in Leiden and Tokyo and the rotational constants of F₂CCH₂, F₂CCHD and F₂CCD₂ derived from the microwave study by Chauffoureaux. The two electron diffraction data agreed without significant discrepancy. From a joint least squares analysis of the diffraction and microwave data, the following r_g bond distances and r_z bond angles were derived: CC = 1.340 ± 0.006 Å, C-F = 1.315 ± 0.003 Å, C-H = 1.091 ± 0.010 Å, ∠C-C-F = 124.7 ± 0.3°, ∠C-C-H = 119.0 ± 0.4°, where the uncertainties represent estimated limits of error.     

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.     

Electron diffraction determination of the vapour phase molecular structure of azetidine, (CH2)3NH

The electron diffraction study of azetidine yielded the following main geometrical parameters (r_a structure): dihedral angle (the angle between the C-C-C and C-N-C planes) φ = 33.1 ± 2.4°, r(C-N) = 1.482 ± 0.006Å, r(C-C) = 1.553 ± 0.009Å, r(C-H) = 1.107 ± 0.003Å, ∠C-N-C = 92.2 ± 0.4°, ∠C-C-C = 86.9 ± 0.4° and ∠C-C-N = 85.8 ± 0.4°.     

Microwave spectrum of 1,2,4-trifluorobenzene

The microwave spectrum of 1,2,4-trifluorobenzene has been observed in the range 12.5–18.0 GHz and 21.5–25.3 GHz at dry-ice temperature and assigned up to angular momentum state J = 39. The ground state rotational constants and the five quartic centrifugal distortion constants thus obtained are (in MHz): à = 3084.0037 ± 0.0108, B? = 1278.3614 ± 0.0062, C? = 903.6989 ± 0.0108, d_j = ( ?4.599 ± 0.621) · 10^?4, d_jk = (5.9757 ± 1.1586) · 10^?3, d_k = (11.4923 ± 2.0886) · 10^?3, d_wj = (4.0 ± 1.0) · 10^?7, d_wk=(?5.8± 1.1) · 10^?6.The small value of Δ = 0.029 (amu Ų) shows that the molecule is planar and an r₀ - structure using a regular hexagonal benzene ring with the bond lengths C-C = 1.397 Å, C-H = 1.084 Å and C-F = 1.312 Å, reproduces the rotational constants.     

Conformational stability of chlorocyclohexane from temperature-dependent FT-IR spectra of xenon solutions, r 0 structural parameters, and vibrational assignment

Variable temperature (?55 to ?105 °C) studies of the infrared spectra (4000–400 cm^?1) of chlorocyclohexane (c-C₆H₁₁Cl) dissolved in liquefied xenon have been carried out. The infrared spectra of the gas and solid have also been recorded from 4000–100 cm^?1. By analyzing six conformer pairs in the xenon solution, a standard enthalpy difference of 132 ± 13 cm^?1 (1.58 ± 0.16 kJ/mol) was obtained with the equatorial conformer the more stable form. At ambient temperature, the abundance of the axial conformer is 34 ± 1%. The potential surface describing the conformational interchange has been determined and the Fourier coefficients were obtained. From MP2 ab initio calculations utilizing various basis sets with and without diffuse functions, the equatorial conformer is predicted to be more stable by 161 ± 18 cm^?1 from the four largest basis set calculations, which is consistent with the experimental results. However, the average from the corresponding B3LYP density functional theory calculations is 274 ± 15 cm^?1 which is certainly too large. By utilizing the previously reported microwave rotational constants for two isotopomers (³⁵Cl, ³⁷Cl) combined with the structural parameters predicted from the MP2(full)/6-311+G(d,p) calculations, adjusted r ₀ structural parameters have been obtained. The determined heavy atom distances for the most stable chair-equatorial conformer in Å are: r ₀(C₁–C₇,₈) = 1.532(3); r ₀(C₇,₈–C₁₃,₁₄) = 1.536(3); r ₀(C₄–C₁₃,₁₄) = 1.524(3); and r ₀(C₄–Cl₆) = 1.802(5) and the angles in degrees: ∠C₁C₇,₈C₁₃,₁₄ = 111.3(5)º; ∠Cl₆C₄C₁₃,₁₄ = 109.7(5)º with the two dihedral angles ∠C₈C₁C₇C₁₃ = 56.3(10)º and ∠C₁₄C₄C₁₃C₇ = 56.7(10)º. These parameters are in good agreement with those reported earlier from microwave and electron diffraction studies where the CC and CH distances were all assumed to be equal. A few of the previously reported vibrational assignments have been corrected. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results for some similar molecules.     

On the molecular structure of (CH3)2NSO2N(CH3)2 as studied by gas electron diffraction

The following bond lengths and bond angles have been deduced from a vapour phase electron diffraction study of (CH₃)₂NSO₂N(CH₃)₂: r(C-H) 1.114 ± 0.005 Å, r(S-O) 1.432 ± 0.010 Å, r(N-C) 1.475 ± 0.013 Å, r(S-N) 1.651 ± 0.003 Å, ∠N-C-H 109.3 ± 2.0°, ∠C-N-C 118.0 ± 302°, ∠S-N-C 115.2 ± 1.1°, ∠N-S-N 110.5±1.3° and ∠O-S-O 114.7±2.5°. The sulphur bond configuration and the prevailing conformation, which was identical to that in the crystal, are discussed in relation to analogous sulphide and sulphoxide derivatives.