Molecular structure of ethynylbenzene from electron diffraction and ab initio molecular orbital calculations

The molecular structure and benzene ring distortions of ethynylbenzene have been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF/6-31G^* and 6-3G^** levels. Least-squares refinement of a model withC _2v, symmetry, with constraints from the MO calculations, yielded the following important bond distances and angles:r _g(C _i -C _o )=1.407±0.003 Å,r _g(C _o -C _m )=1.397±0.003 Å,r _g(C _m -C _p )=1.400±0.003 Å,r _g(Cr _i -CCH)=1.436 ±0.004 Å,r _g(C=C)=1.205±0.005 Å, C _o -C _i -C _o =119.8±0.4°. The deformation of the benzene ring of ethynylbenzene given by the MO calculations, including o-C_i-C_o=119.4°, is insensitive to the basis set used and agrees with that obtained by low-temperature X-ray crystallography for the phenylethynyl fragment, C₆H₅-CC-, in two different crystal environments. The partial substitution structure of ethynylbenzene from microwave spectroscopy is shown to be inaccurate in the ipso region of the benzene ring.     

Gas-phase electron diffraction studies of the molecular structures of pentafluoroethane,C2F5H,and monofluoroethane,C2H5F

The molecular structures of C₂F₅H and C₂H₅F have been studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument. The following values for the main independent geometrical parameters were obtained (r_a values with e.s.d. in parentheses): in C₂F₅H, C-C = 1.525(4) Å, C-F(CHF₂) = 1.347 Å, C-F(CF₃) = 1.327 Å [C-F(av.) = 1.335(2) Å], ∠CCF(av.) = 110.0(2)°; in C₂H₅F, C-C = 1.502(5) Å, C-F = 1.397(4) Å, C-H = 1.097(2) Å. ∠CCF = 110.4(2)°, ∠CCH(av.) = 113.6(4)°. Evidence is presented to show that the electron diffraction data for C₂H₅F are not compatible with values for the bond angles deduced spectroscopically.     

Zero-point average structures of acetyl chloride and acetyl bromide

The zero-point average structures of acetyl chloride and acetyl bromide have been determined by the combined use of their moments of inertia and average distances, obtained by means of microwave spectroscopy and electron diffraction. The r_z parameters determined are as follows: r_z(CO) = 1.185 ± 0.003 Å, r_z(C-Cl) = 1.796 ± 0.002 Å, r_z(C-C) = 1.505 ± 0.003 Å, r_z(C-H) = 1.092 ± 0.005 Å, φ_z(OCCl) = 121.2 ± 0.6°, φ_z(CCCl) = 111.6 ± 0.6°, φ_z(HCH) = 108.8 ± 0.8° and tilt(CH3) = 1.3 ± 1.0°, for chloride; r_z(CO) = 1.181 ± 0.003 Å, r_z(C-Br) = 1.974 ± 0.003 Å, r_z(C-C) = 1.516 ± 0.003 Å, φ_z(OCBr) = 122.3 ± 1.5°, φ_z(CCBr) = 111.0 ± 1.5°, φ_z(HCH) = 109.9 ± 1.1°, tilt(CH₃) = 1.9 ± 1.0°, for bromide. The barriers V₃ to internal rotation have been revised to 1260 and 1256 cal mol⁻¹ for the chloride and bromide, respectively.     

The gas-phase rotamers of 1,1,2,2-tetrafluoroethane - force field,vibrational amplitudes and geometry - a joint electron-diffraction and spectroscopic study

The gas-phase conformational mixture of the anti and gauche rotamers of 1,1,2,2-tetrafluoroethane has been subjected to an electron-diffraction study at 253 K. Effective least-squares refinement of the geometry and relative proportions of the conformers was achieved with vibrational amplitudes for both conformers fixed at values calculated from spectroscopic data. In order to calculate the amplitudes, a force field was deduced which reproduced the observed wave numbers for both conformers; the assignment of the modes proposed in the literature was modified slightly. At 253 K, the rotamer composition was found to be 84% anti : 16%gauche, which corresponds to an energy difference of 1170 cal mol^?1; the geometrical parameters (r_a values) and e.s.d. are C-C = 1.518 ± 0.005 Å, C-H = 1.098 ± 0.006 Å, C-F = 1.350 ± 0.002 Å. ∠CCF = 108.2 ± 0.3°, ∠FCF = 107.3 ± 0-3°, ∠ CCH = 110.3 ± 1.0δ, and the torsion angleτ _hcch in the gauche form is 78 ± 2°.     

A gas-phase electron diffraction study op the molecular structure of 1,1,1,2-tetrafluoroethane

The molecular structure of 1,1,1,2-tetrafluoroethane is studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument. Effective least-squares refinement of the geometry is achieved with values for vibrational amplitudes transferred from normal coordinate calculations on related molecules. The following values for the main independent geometrical parameters are obtained (r_a values with e.s.d. in parentheses): C-C = 1.501(4) Å, C-H = 1.077 (15) Å, C-F(CH₂F) = 1.389(6) Å, C-F(CF₃) = 1.334 (2) Å, ∠CCH= 106.1(12)°, ∠CCF(CH₂F)= 112.3(4) Å, ∠CCF(CF₃)= 110.4(2). Other angles are ∠FCF = 108.6 (2)° and ∠FCH = 111.4(15)°, with ∠HCH constrained at 109.4°. The r_a bond lengths of all the fluoroethanes are compared.     

Preparation and properties of iron vanadium telluride,FeV2Te4

Iron vanadium telluride, FeV₂Te₄, has been prepared and found to have the monoclinic defect NiAs type structure with unit cell parameters a₀ = 6.641 ± 0.005Å, b₀ = 3.727 ± 0.005Å, c₀ = 12.36 ± 0.01Å, β = 91.75 ± 0.05°. Electrical resistance measurements show FeV₂Te₄ to be metallic, and magnetic susceptibility vs. temperature data indicate magnetic ordering at approximately 5°K.     

Molecular structure of 1,1-dimethylsilacyclopentene-3,4-oxide from gas-phase electron diffraction

The molecular structure of 1,1-dimethylsilacyclopentene-3,4-oxide has been determined by electron diffraction in the gas phase. The experimental data are consistent withC _s molecular symmetry and boat conformation with a flattened end at the silicon atom. The flap angles characterizing the orientation of C-Si-C and C-O-C planes with respect to the four coplanar carbon atoms of the ring are 16.6 ± 0.6 and 73.3 ± 0.6, respectively. Bond lengths (r_g) are Si-C₆, 1.866 ±0.008; Si-C₂, 1.899 ± 0.008; C₂-C₃, 1.513 ± 0.005; C₃-C₄ (bridge), 1.477 ± 0.013; C-O, 1.443 ± 0.007; (C-H)_mean 1.116 ± 0.003 å. Bond angles are <C₅-Si-C₂, 96.2 ± 0.4; <Si-C₂-C₃, 103.9 ± 0.3; <C₂-C₃-C₄, 116.5 ± 0.3; <C₃-C₄-O, 59.2 ± 0.5; zC₄-C₃-H₉, 109.0 ± 3.5; <C₂-C₃-H₉, 132.9 ± 3.1; <C₆-Si-C₁₂, 114.6 ± 0.8; <Si-C₆-H₁₅, 109.7 ± 0.9.     

Molecular Structure of 1,3,5-Tris (Trimethylstannyl) Benzene: An Electron Diffraction Study

The molecular structure of 1,3,5-tris (trimethylstannyl) benzene has been determined by gas-phase electron diffraction. The C — C bond length is in good agreement with that in benzene. In agreement with the somewhat electron-releasing character of the substituents, the endocyclic bond angles at the substituents are somewhat smaller than 120°. The mean value of Sn — C bond lengths is greater than that in tetraphenyltin and tetramethyltin. The SnMe₃ groups appear freely rotating around the C_aryl — Sn bonds. The following bond lengths (r _g) and bond angles were determined: (Sn — C)_mean 2.150 ± 0.007 Å, C — C 1.399 ± 0.005 Å, (C — H)_mean 1.105 ± 0.006 Å, < C — C(Sn) — C 117.7 ± 1.7º, < C_aryl — Sn — C_methyl 106.7 ± 0.7º < Sn — C — H 111.5 ± 0.9º.     

Microwave spectrum,structure, dipole moment and barrier to internal rotation of methyltrifluorosilane

The rotational spectrum of methyltrifluorosilane in the ground and the first three excited states of the torsional mode have been investigated in the region of 12.5–40.0 GHz. The rotational transitions for the ¹³C isotopic species have also been measured. The following structural parameters have been determined: r(CH) = 1.081 ± 0.004 Å, ∠ HCSi = 111°1' ± 30', r(CSi) = 1.812±0.014 Å, r(SiF) = 1.574 ± 0.007 Å, ∠ FSiC = 112°20'± 1°6'. The structural parameters are compared to the corresponding ones for similar molecules. The dipole moment was determined to be 2.33 ± 0.10 D. From relative intensity measurements, the barrier to internal rotation was found to be 0.93 ± 0.09 kcal mol⁻¹; this value is consistent with the values obtained for other methylfluorosilanes.     

Structural determination of carvone, a component of spearmint, by means of gas electron diffraction augmented by theoretical calculations

The molecular structure and conformation of carvone, a compound with a minty odor, were investigated by means of gas electron diffraction supported by theoretical calculations. Electron diffraction patterns were recorded by heating the nozzle up to 128 °C to obtain enough scattering intensity. The infrared spectrum was also measured by using an absorption cell with a path length of 10 m. The obtained molecular scattering intensities were analyzed with the aid of theoretical calculations and infrared spectroscopy. It was revealed that the experimental data are well reproduced by assuming that carvone consists of a mixture of three conformers that have the isopropenyl group in the equatorial position and mutually differ in the torsional angle around the single bond connecting the ring and the isopropenyl group. It was also found that the puckering amplitude of the ring of carvone is close to those of menthol and isomenthol, a minty compound and its nonminty isomer. The determined structural parameters (r_g and ∠_α) of the most abundant conformer of carvone are as follows: 〈r(C-C)〉=1.520(3) Å; 〈r(CC)〉=1.360(5) Å; r(CO)=1.225(5) Å; 〈r(C-H)〉=1.104(4)Å; 〈∠CC-C〉=121.1(5)°; 〈∠C-C-C〉=110.4(5)°; ∠C-CO-C=117.1(14)°; 〈∠C-C-H〉=111.1(13)°. Angle brackets denote average values and parenthesized values are the estimated limits of error (3σ) referring to the last significant digit.     

The gas-phase molecular structure of 1-fluorosilatrane from electron diffraction

The molecular geometry of 1-fluorosilatrane has been determined by gas-phase electron diffraction. The distance between the nitrogen and silicon atoms is much longer in the gas phase, viz., 2.324±0.014 Å, than in the crystal, 2.042 (1) Å [5]. This indicates a weakened donor-acceptor interaction possibly as a consequence of the absence of intermolecular interactions in the gas phase. The five-membered rings take envelope conformations with the carbon atoms adjacent to nitrogen at the envelope tips. The following bond distances ( _g , Å) and bond angles (°) were obtained with their estimated total errors: N-C, 1.481±0.008; C-C, 1.514±0.011; O-C, 1.392±0.004; Si-O, 1.652±0.003; Si-F, 1.568±0.006; C-H, 1.118±0.005; N-C-C, 104.5±0.6; C-C-O, 117.0±0.7;C-O-Si, 123.7±0.6; O-Si-F, 98.7±0.3; O-Si-O, 117.8±0.1; C-N-C, 115.0±0.3.     

Gas-phase electron diffraction study of cyclic dimer of dimethylphosphinic acid (Me2P(O)OH)2 using quantum chemical data and a priori force field

The molecular structure of the hydrogen bonded cyclic dimer of dimethylphosphinic acid (Me₂P(O)OH)₂ was determined by gas-phase electron diffraction (GED) at 433 K. The presence of monomer cannot be determined at this temperature within the error limits for the GED method. Structural analysis was performed with consideration of non-linear kinematic effects at the first-order level of perturbation theory (h1). The vibrational characteristics of internuclear distances were calculated from a priori scaled quantum chemical (RHF/6-311G**) force field. The analysis aided by a constraint based on the RHF/6-311G** calculations yielded the following r_h1-parameters of the C₂-symmetry dimer configuration: PO 1.497(3); P-O 1.573(4); P-C 1.806(1) and 1.811(1) Å; (C-H)_av. 1.109(3) Å; ∠O-PO 120(1)°. Unlike PO and P-O bonds, whose lengths in the gas phase and in the solid state differ insignificantly, the -O?O distance in the gas phase (r_h1 2.81(4) Å) is considerably longer than in the solid state (r_α 2.48(2) Å). The latter is in accordance with the conclusion based on the IR spectra that transition from gas to a solid sample leads to strengthening of the H-bonds. Due to its small contribution to the diffraction pattern, the donor O-H bond length (r_h1 0.99(1) Å) was forcedly bound up with the parameters of C-H bonds. With this assumption, the other geometrical parameters characterizing the H-bond fragment have the following r_h1 values: O?H 1.84(4) Å, ∠-OHO164(6)°, and ∠P-O-H 117(4)°. Conformational flexibility of the non-planar eight-atom ring of the dimer is experimentally verified by absence of any apparent peaks of the f(r) curve at the r-region of more than 4.2 Å.     

Molecular structure and conformational composition of 1-Chlorobutane, 1-Bromobutane,and 1-Iodobutane as determined by gas-phase electron diffraction and ab initio calculations

Gas-phase electron diffraction (ED), together with ab initio molecular orbital calculations, have been used to determine the structure and conformational composition of 1-chlorobutane, 1-bromobutane, and 1-iodobutane. These molecules may in principle exist as mixtures of five different conformers, but only three or four of these were observed in gas phase at temperatures of the ED experiments, 18C, 18C, and 23C, respectively. The observed conformational compositions (1-chlorobutane, 1-bromobutane, and 1-iodobutane) were AA (13 ± 12%, 21 ± 14%, 19 ± 17%), GA (60±13%, 33±32%, 17±31%), AG (12±16%, 8±12%, <1%), and GG (12 ±16%, 38± 34%, 64±31%). A and G denotesanti andgauche positions for the X-C₁-C₂-C₃ (X=Cl, Br, I), and the C₁-C₂-C₃-C₄ torsion angles. The results for the most important distances (r _g) and angles () from the combined ED/ab initio study for the GA conformer of 1-chlorobutane, with estimated 2 uncertainties, arer(C₁-C₂)=1.519(3)å,r (C₂-C₃)=1.530(3) å,r (C₃-C₄)=1.543(3) å,r (C₁-Cl)=1.800(4) å, <C₁C₂C₃=114.3(6), <C₂C₃C₄=112.0(6), <CCCl=112.3(5). The results for the GA conformer of 1-bromobutane arer (C₁-C₂)=1.513(4) å,r (C₂-C₃)=1.526(4) å,r (C₃-C₄)=1.540(4) å,r(C₁-Br)=1.959(8) å, <C₁C₂C₃=115.3(11), <C₂C₃C₄=112.8(11),<CCBr=112.1(14). The results for 1-chlorobutane and 1-bromobutane are compared with those from earlier electron diffraction investigations. The results for the GA conformer of 1-iodobutane arer (C₁-C₂)=1.506(5) å,r (C₂-C₃)=1.518(5) å,r (C₃-C₄)=1.535(5) å,r (C₁-I)=2.133(11) å, <C₁C₂C₃=116.8(15), <C₂C₃C₄=115.3(15), <CCI=110.2(14). Differences in length between the different C-H bonds in each molecule, between the different C-C bonds, between the different CCH angles, and between the different CCC angles were kept constant at the values obtained from the ab initio calculations.     

The molecular structures of mono-substituted cl-cyclohexene by gas-phase electron diffraction

The molecular structures of mono-substituted chlorocyclohexene are determined by gas-phase electron diffraction. The structural parameters are obtained by applying leastsquares analysis to the molecular scattering intensities. The bond distances (r_g) and bond angles are: (1) 1-Cl-cyclohexene: C₁C₂ = 1.336 ± 0.006 Å. C₂-C₃ = 1.500 ± 0.009 Å, C₃-C₄ = 1.533 ± 0.010 Å, C₄-C₅ = 1.537 Å, C₅-C₆ = 1.527 ± 0.010 Å, C₁-C₆ = 1.504 ± 0.009 Å. C-Cl = 1.747 ± 0.005 Å, C-H_av = 1.138 ± 0.010 Å, ∠Cl-cc = 126.3 ± 0.5°, ∠C₆C₁C₂ = 123.9 ± 0.8°. ∠C₁C₂C₃= 124.6 ± 0.8°, ∠C₄C₃C₂ = 111.8 ± 1.2° and ∠-C₅C₆C₁ = 111.3 ± 1.1°; (2) 3-Cl-cyclohexene: C₁=C₂ = 1.336 Å, C₂-C₃ = 1.501 ± 0.010 Å, C₃-C₄ = 1.513 ± 0.008 Å, C₄-C₅ = 1.542 Å, C₅-C₆, = 1.516 ± 0.007 Å, C₁-C₆ = 1.505 ± 0.006 Å, C-C1 = 1.801 ± 0.005 Å, C-H_av = 1.120 ± 0.008 Å, ∠C₆C₁C₂ = 123.2 ± 1.0°, ∠C₁C₂C₃ = 124.1 ± 1.7°, ∠C₅C₆C₁ = 113.0 ± 1.3°, ∠C₂C₃C₄ = 112.5 ± 1.5° ∠ClC₃C₂ = 110.3 ± 0.8°, ∠H-C=C = 123.0 ± 3.0° and ǒH-C-C = 109.5 ± 2.0°, with a mixture of 55% axial and 45% equatorial conformers; (3) 4-Cl-cyclohexene: C₁=C₂ = 1.336 Å, C₂-C₃ = 1.507 ± 0.007 Å, C₃-C₄ = 1.516 ± 0.008 Å, C₄-C₅ = 1.544 Å, C₅-C₆ = 1.523 ± 0.010 Å, C₁- C₆ = 1-507 Å, C-Cl = 1.799 ± 0.005 Å, C-H_av = 1.116 ± 0.005 Å, ∠C₆C₁C₂ = 123.3 ± 1.5°, ∠C₅C₆C₁ = 113.0 ± 1.0°, ∠C₂C₃C₄ = 112.3 ± 1.0°, ∠ClC₄C₃ = 110.2 ± 2.0°, ∠H-CC = 117.1 ± 4.5° and ∠H-C-C = 109.5 ± 1.0°, with a mixture of 45% axial and 55% equatorial conformers.     

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°.     

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.     

Beitrag zur Synthese des Hydroxylammoniumfluorids

Summary Hydroxylammonium fluoride was prepared in aqueous solution by the reaction of hydroxylamine with aqueous hydrogen fluoride. The solubility in water (148.7 g/100 g) and ethanol (0.146 g/100 g), the density (1.621±0.005 g/cm³) and the metling point (97.8±2 °C) of the compound have been determined. [NH₃OH]F crystallizes orthorombic, P_abc,a=6.490(1) Å,b=9.799(1) Å,c=13.519(2) Å.

     

Synthesis, characterization and the crystal structure of 1-[(N-methyl-N-aryl)amino]ethylferrocenes

The reactions of ferrocenylketimines [(η⁵-C₅H₄CCH₃NAr)Fe(η⁵-C₅H₅)] (Ar=a variety of substituted phenyls) with methyl-iodide in refluxed dichloromethane followed by reduction with sodium borohydride in absolute ethanol led to [(η⁵-C₅H₄CH(CH₃)N(CH₃)Ar)Fe(η⁵-C₅H₅)]. Compound [(η⁵-C₅H₄CH(CH₃)N(CH₃)C₆H₄Cl-p)Fe(η⁵-C₅H₅)] (3d) has been characterized structurally. Compound 3d is monoclinic, space group P2₁/n, with a=8.908(2) Å, b=13.63(1) Å, c=14.510(3) Å and β=107.03°.     

The molecular structure of gaseous tetrafluoro-p-benzoquinone and tetramethyl-p-benzoquinone as determined by electron diffraction

The molecular structures of gaseous tetrafluoro-p-benzoquinone (p-fluoranil) and tetramethyl-p-benzoquinone (duroquinone) have been investigated by electron diffraction. Except for the methyl group hydrogen atoms, the molecules are planar to within experimental error, but small deviations from planarity are completely compatible with the data. Values for the geometrical parameters (r_adistances and r_α with parenthesized uncertainties of 2σ including estimated uncertainty in the electron wavelength and correlation effects, are as follows. Tetrafluoro-p-benzoquinone: D_2h symmetry (assumed); r(C0) = 1.211(6) Å, r(CC) = 1.339(12) Å, r(C-C) = 1.489(5') Å, r(C-F) = 1.323(5) Å, ∠C-C-C = 116.8(7)° and ∠C-C-F = 116.1(7)°. Tetramethyl-p-benzoquinone: C_2h symmetry (assumed);r(C-H) = 1.102(18) Å, r(CO) = 1.229(8) Å, r(CC) = 1.352(8) Å, r(C_sp2-C_sp2) = 1.491(11) Å, r(C_sp2-C_sp3) = 1.504(12) A, ∠C-CO-C = 120.8(8)°. ∠C-C-CH₃ = 116.1(8)°, ∠C-C-H = 110.5(34)° and α₁ = α₂ (methyl torsion = 30° (assumed).