Molecular structures of propene and 3,3,3-trifluoropropene determined by gas electron diffraction

The structures of propene and 3,3,3-trifluoropropene have been studied by electron diffraction intensities measured in the present study and rotational constants reported in the literature. The following average structures have been determined: For propene, r_g(CC) = 1.342 ± 0.002 Å, r_g(C-C) = 1.506 ± 0.003 Å, r_g(C-H)_vinyl = 1.104 ± 0.010 Å, r_g(C-H)_methyl = 1.117 ± 0.008 Å, ∠(C-CC) = 124.3 ± 0.4°, ∠(CC-H) = 121.3 ± 1.4°, and ∠(C-C-H) = 110.7 ± 0.9°; for trifluoropropene, r_g(CC) = 1.318 ± 0.008 Å, r_g(C-C) = 1.495 ± 0.006 Å, r_g(C-H)= 1.100 ± 0.018 Å, r_g(C-F) = 1.347 ± 0.003 Å, ∠(C-CC) = 125.8 + 1.1°, ∠(C-C-F) = 112.0 ± 0.2°, where the valence angles refer to the r_av structure, and the uncertainties represent estimated limits of experimental error. A simple set of quadratic force constants for each molecule has been estimated. Regular trends have been observed in the CC and C-C bond distances and the C-CC angles in these and related molecules. Significant differences between the CC, C-C and C-F distances and the C-C-F angle in trifluoropropene and in hexafluoroisobutene reported by Hilderbrandt et al. have been indicated.     

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.     

Molecular structures of acetyl fluoride and acetyl iodide

The molecular structures of acetyl fluoride and acetyl iodide have been determined by making use of the average distances obtained in the present study together with the moments of inertia reported in the literature. The large amplitude theory for a molecule with an internal top was used in the joint analysis. The thermal-average values of internuclear distances r_g and the bond angles in the zero-point average structure Φ_z are as follows: r_g(C-O) = 1.185 ±0.002 $\text{}\text{?}$rA, r_g(C-F) = 1.362± 0.002 Å, r_g(C-C) = 1.505±0.002 Å, r_g(C-H) = 1.101 ±0.004 Å, Φ_z(OCF) = 120.7°±0.4°,Φ_z(CCF) = 110.5° ± 0.5°, Φ_z(HCH) = 109.3°±0.6° tilt(CH₃) = 0.1°±1°, for acetyl fluoride; r_g(C=O) = 1.198±0.013 $\text{}\text{?}$rA, r_g(C-I) = 2.217±0.009 Å, r_g(C-C) = 1.492±0.015 $\text{}\text{?}$rA, r_g(C-H) = 1.101 ± 0.004 Å, Φ_z(OCI) = 119.5°± 0.8°,Φ_z(CCI) = 111.7°±0.9°, Φ_z(HCH) = 110.8°±0.8° and tilt(CH₃) = 1.7°+5.4° for acetyl iodide. The uncertainties represent the estimated limits of error. The barriers V₃ to internal rotation have been reanalyzed making use of the effective moments of inertia of the methyl top estimated on the basis of the large amplitude theory and resulted in 1039 and 1176 cal mol^?1 for acetyl fluoride and acetyl iodide, respectively. The structure parameters have been compared with those of other CH₃COX (X = Cl, Br, H, CH₃) type molecules.     

Molecular structures of isobutene and 2,3-dimethyl-2-butene as studied by gas electron diffraction

The structures of isobutene and 2,3-dimethyl-2-butene have been studied by gas electron diffraction. For isobutene the rotational constants obtained by Laurie by microwave spectroscopy have also been taken into account. Leastsquares analyses have given the following r_g bond distances and valence angles (r_av for isobutene and r_α for dimethylbutene): for isobutene, r(CC) = 1.342±0.003 Å, r(C-C)= 1.508±0.002Å, r(C-H, methyl) = 1.119±0.007 Å, r(C-H, methylene) = 1.095±0.020 Å, ∠(C-CC) = 122.2±0.2°, ∠(H-C-H) = 107.9±0.8°, and ∠(C-C-H) 121.3±1.5°; for dimethylbutene, r(CC)= 1.353 ±0.004 Å, r(C-C) = 1.511±0.002 Å, r(C-H) = 1.118± 0.004 Å, ∠(C-CC)= 123.9±0.5°, and ∠(H-C-H)= 107.0±1.0°, where the uncertainties represent estimated limits of experimental error. The bond distances and valence angles in these molecules and in related molecules are compared with one another. The CC and C-C bond distances increase almost regularly with the number of methyl groups, and the C-C bonds in isobutene and dimethylbutene are shorter than those in acetaldehyde and acetone by about 0.01 Å. Systematic variations in the C-CC angles suggest the steric influence of methyl groups.     

Microwave spectrum and molecular structure of arsenic tribromide1

The microwave spectrum of arsenic tribromide has been recorded in the frequency range 26.5–40.0 GHz. From the rotational constants for the symmetric top species ⁷⁹AsBr₃ and ⁸¹AsBr₃ the following structural parameters have been deduced: r_z(AsBr) = 2.324 ± 0.003 Å, θ_z(BrAsBr) = 99.8 ± 0.2°. These results are in excellent agreement with the parameters obtained by Samdal et al., in a concurrent electron diffraction study.     

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°.     

Microwave spectroscopic study on the molecular structure and the quadrupole coupling constants of thionyl chloride

Microwave spectra of thionyl chloride, SO³⁵Cl₂ and SO³⁵Cl³⁷Cl, in the frequency range 8–25 GHz have been analyzed. The rotational constants have been obtained from the low J transition frequencies. The r_S coordinates of Cl atoms and the r_o structure have been evaluated with some assumptions: r(S-O) = 1.435 ± 0.011± Å, r(S—Cl) = 2.072 0.005 Å, ∠ OSCl = 108.00 ± 0.06°, ∠ ClSCl = 97.15 ± 0.30°. Nuclear quadrupole coupling constants have been obtained for the SO³⁵Cl₂, species: x_aa = ?25.02 ± 0.04 MHz, x(_bb = ?0.25 ± 0.04 MHz, X_cc = 25.27 ± 0.08 MHz, and X_zz = ?96.75 MHz. The values obtained are compared with those of other workers.     

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'.     

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.     

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.     

The molecular structure of trifluoroethene in the gas-phase as determined from electron diffraction and microwave data

The molecular structure of trifluoroethene was determined from electron diffraction data and the microwave rotational constants of the parent and deuterated molecule, corrected for zero-point vibrational motion. A GVFF adjusted to fit the vibrational frequencies was used for the correction. The molecule was found to be planar. Assuming equal geminal C1—F bond lengths, the following r_g distances and r_av angles are found: C1—F = 1.316 ± 0.011 Å, C2—F = 1.342 ± 0.024 Å, CC = 1.341 ± 0.012 Å, C—H = 1.100 ± 0.02 Å, ∠C—C—F1 = 123.1 ± 1.5°. ∠C—C—F2 = 124.0 ± 0.6°, ∠C—C—F3 = 120 ± 0.7° (Fl trans to F3) and ∠C—C—H = 124.0 ± 1.7°.The error limits include 3σ (σ = estimated standard deviation) and estimates of the systematic errors. The analysis suggests that all the C1—F distances are not equivalent, neither are the C2—C1—F angles, though the differences are not significant (10% level).     

The structure of bis(1,1,1,5.5,5-hexafluoro-2,4. pentadionato) copper(II) as determined by gas phase electron diffraction

The r_g structure of bis(1,1,1,5,5,5-hexafluoroacetylacetonato) copper(II) has been determined by gas phase electron diffraction. The experimental data were found to be consistent with a D_2h model in which the oxygens from the two ligands are arranged in an essentially square planar configuration about the copper atom (∠OCuO = 90.6° ± 1.2°). It was possible to obtain a precise value for the copper oxygen bond length, r_g = 1.919 ± 0.008 Å, since this distance appeared as an isolated peak in the radial distribution curve. Structural parameters for the ligand (r_g(C-O) = 1.276 ± 0.009 Å, r_g(C-C_ring) = 1.392 ± 0.015 Å, r_g(C-CF₃)= 1.558 ± 0.009 Å and r_g(C-F) = 1.339 ± 0.003 Å), while less precisely determined are, nevertheless, consistent with reported values for related molecules. A model for the rotational isomerism of the four CF₃ groups was invoked in order to explain various features in the radial distribution curve in a region from 2.5 to 5.5 Å.     

An improved electron diffraction—microwave and molecular orbital study of the structure of SF5Cl

A new study of the structure of SF₅Cl is reported. Previously-obtained electron diffraction data have been corrected for multiple scattering, and newly-reported microwave rotational constants have been combined in the analysis. Structural parameters, with estimated limits of error, were found to be r_g (S-Cl) 2.055(1) Å, r_g (S-F)_mean 1.570(1) Å, r_g (S-F_ax) - r_g(S-F_eq) 0.001(8) Å, r_g(S-F_eq) 1.571(3) Å, r_g (S-F_ax) 1.571(8) Å, ∠α Cl-S-F_eq 90.4(0.1)°. The new data are more self-consistent than was previously the case. Ab initio molecular calculations using three different basis sets are reported and discussed.     

Molecular structure of bis(acetylacetonato)nickel(II) in the gas phase as determined from electron diffraction data

The molecular structure of bis(acetylacetonato)nickel(II) has been determined by a sector-microphotometer gaseous electron-diffraction method. The experimental data were found to be consistent with a monomeric square-planar structure. The structural parameters of the chelate were determined as follows: ∠ ONiO = 93.6 ± 1.1°, r_g(Ni-O) = 1.876±0.005A Å, r_g(C-0) = 1.273± 0.007 Å, r_g(C-C_ring) = 1.401 ± 0.010 Å, r_g(C-C_methyl) = 1.504 ± 0.013 Å. The mean amplitudes of vibration and the shrinkage effects were calculated from normal-vibration treatment using the Urey-Bradley force field.     

Molecular structure and microwave spectra of isotopic chloro-, bromo-, and iodocyanoacetylene

The microwave spectra of the halogeno-cyanoacetylenes, X-CC-CN (X = ¹²⁷I, ⁸¹Br, ⁷⁹Br, ³⁷Cl, ³⁵Cl), have been investigated. The molecules were found to be linear. The vibration-rotation constants of the three bending vibrations and the lower stretching vibration were determined. Lines belonging to the monosubstituted ¹³C and ¹⁵N species in their natural abundances were measured and the rotational constants obtained. The bond distances based on the substitution coordinates were: for I-CC-CN r(I-C) = 1.984₆ Å, r(CC) = 1.207_o Å, r(C-C) = 1.370₂ Å, r(CN) = l.l60₄ Å; for Br-CC-CN, r(Br-C) = 1.785₈ Å, r(CC) = 1.204₁ Å, r(C-C) = 1.369₉ Å, r(CN) = 1.159₃ Å; and for C1-CC-CN, r(Cl-C) = 1.624₅ Å, r(CC) = 1.209_o Å, r(C-C) = 1.369_o Å, r(CN) = 1.160₂ Å.     

An electron-diffraction study of the molecular structure of gaseous perbromyl fluoride and calculation of its force field and vibrational amplitudes

The molecular structure of FBrO₃ has been studied by gas-phase electron diffraction. Least-squares refinements of the molecular geometry using fixed spectroscopic amplitudes revealed two geometrical minima. Initially, the amplitudes employed were derived from diagonal force fields obtained by spectroscopic least-squares refinements to fit observed and calculated wave numbers; for each geometry there are two spectroscopic minima. In the lowest geometrical minimum the wave number agreement is poor, however, the introduction of the ∠OBrO/∠FBrO interaction force constant removed the discrepancies; the resulting force field is F(Br-O) = 6.92 ± 0.02 mdyn Å^?1F(Br-F) = 3.22 ± 0.03 mdyn Å^?1, F(∠OBrO) = 1.06 ± 0.02 mdyn Å, F(∠FBrO) = 0.81 ± 0.03 mdyn Å, F(∠OBrO/∠FBrO) = ?0.19 ± 0.02 mdyn Å. In the corresponding geometrical minimum r_g(Br-O) = 1.582 ± 0.001 Å, r_g(Br-F) = 1.708 ± 0.003 Å, r_α(∠OBrO) = 114.9 ± 0.3°, r_α(∠FBrO) = 103.3 ± 0.3°. Perpendicular amplitude correction coefficients, calculated for each force field employed, were used throughout to relate the interatomic distances through the r_α-structure. The geometries of the r_α^o- and r_e-structures are estimated.     

Molecular structure of carbonyl bromide as studied by gas electron diffraction

The molecular structure of COBr₂ has been determined as follows by an analysis of electron diffraction intensity: r_g(CO) = 1.178 ± 0.009 Å, r_g(C-Br) = 1.923 ± 0.005 Å and θ°_α(Br-C-Br) = 112.3 ± 0.4°. The uncertainties represent estimated limits of error. The observed systematic trends in the bond lengths and bond angles in carbonyl and thiocarbonyl halides are discussed.     

The molecular structure of pyrazine as determined from gas-phase electron diffraction data

The structure of pyrazine (1,4 diazabenzene, C₄H₄N₄) has been determined at 333 K by means of gas-phase electron diffraction. The r_g parameters are as follows: r(C-C) = 1.339 ± 0.002 Å. r(C-N) = 1.403 ± 0.004 Å, r(C-H) = 1.115 ± 0.004 Å. ∠C-C-N = 115.6 ± 0.4°, and ∠C-C-H = 123.9 ± 0.6° (error limits are 2.5σ). At a 10% level the r_α structure does not differ significantly from the structure in the solid state, so long as high order X-ray, results corrected for librational motion are used; otherwise significantly different results are found even at the 1% level. Calculated and observed mean square amplitudes compare favourably.     

Molecular structure of bis(acetylacetonato)beryllium in the gas phase as determined from electron diffraction data

The molecular structure of bis(acetylacetonato)beryllium has been determined by gas electron diffraction. The experimental data were found to be consistent with the D_2d model in which the oxygen atoms are arranged tetrahedrally around the central beryllium atom (∠OBeO = 106.0 ± 1.0°). The structural parameters are as follows: r_g(Be-O) = 1.615 ± 0.006 Å, r_g (C-O) = 1.270 ± 0.004 Å, r_g (C-C_ring) = 1.397 ± 0.004 Å, r_g (C-C_meth) = 1.499 ± 0.005 Å. The mean amplitudes of vibration were calculated from the normal-vibration treatment using the modified Urey—Bradley force field     

Simple isotopic product rules valid for absolute and integrated infrared intensities

Microwave spectra of CH¹⁸ OCOOH, CHOC¹⁸ OOH, CHOCO¹⁸ OH, ¹³ CHOCOOH and CHO¹³ COOH are reported and have been used in combination with data on CHOCOOH and CHOCOOD to determine the molecular structure as r(C=O)_ald. = 1.174 ± 0.006 Å, r(C=O)_acid = 1.203 ±0.006 Å, r(C—O) = 1.313 ± 0.010 Å, r(C—C) = 1.535 ± 0.005 Å, r(O—H) = 0.948 ± 0.004 Å, r(C—H) = 1.104 ±0.010 Å, ald. = 123.7 ± 0.4<, 相似文献