Electron diffraction study of the thionyl fluoride molecular structure

The electron diffraction study of thionyl fluoride yielded the following geometrical parameters (r_a structure): S-O 1.420±0.003 Å, S-F 1.583±0.003Å, O-S-F 106.2±0.2° and F-S-F 92.2±0.3°. The average structure (r_α°) is also given. Some of the variations in the molecular geometries of SOX₂ and SO₂X₂ molecules (X = F or Cl) involving the valence shell electron pair repulsion theory are discussed.     

Electron diffraction study of molecular structure of mebicar

The structure of the mebicar molecule has been studied by gas-phase electron-diffractometry using quantum chemical calculations. An eclipsed conformation along the C-C bond (torsion angle ?(H-C-C-H) = 10°) and flattened semi-chair conformations of cyclic fragments have been found. The bond lengths (r _g ) and angles (∠α) show the following average values: r(C-C) 1.576(3) Å, r(C-N) 1.460(3) Å, r(C(O)-N) 1.390(4) Å, r(C=O) 1.211(5) Å, r(C-H) 1.090(5) Å, ∠CCN 103.0(5)°, ∠CNC(O) 112.2(1)°, ∠CNC 122.4(1)°. The dihedral angle between the cyclic fragments is 116.6°.     

Electron diffraction study on the molecular structure of methyltrimethoxysilane

The electron diffraction data for methyltrimethoxysilane are consistent with a C₃ symmetry model, the predominant forms of which have rotational angle(s) between 100 and 155° around the SiO bond (the anti conformation of the CSiOC chain would respond to 0°). There is probably large amplitude motion around the SiO bonds. The following bond lengths and bond angles were determined: r_a(CH) 1.093 ± 0.005, r_a(SiC) 1.842 ± 0.013, r_a(SiO) 1.632 ± 0.004, r_a(OC) 1.425 ± 0.004 », ∠CSiO 109.6 ± 0.5°. and ∠SiOC 123.6 ± 0.5°.     

Electron diffraction study of the molecular structure of cesium metaborate

The molecular structure of cesium metabomte is studied by gas phase electrvn diffruction. The molecule has C_π symmetry with mean intemuclear distances (T_exp= 1080(10) K) R_g(Cs-O) = 269.2(15) pm, R_g(CS...B) = 360(6) pm, α_gα_g(CsOB) = 125(1)°. It is found that the deformation frequency V(CsOB) = 57(5) cm⁻¹. Translated from Zhumal Struktumoi Khimii, Vol. 41, No. 1, pp. 67-73, 2000.     

Electron diffraction study of the structure the NbBr4 molecule

The structure of the NbBr₄ molecule is studied in synchronous electron diffraction and mass spectrometry experiments. Gaseous niobium tetrabromide is synthesized in the course of the experiment during the interaction of niobium chips with bromine at 496°C. Analysis of the geometrical models of the NbBr₄ molecules of C_2v, C_3v, D_2d, and T_d symmetries shows that the tetrahedral model is preferable. The thermally averaged parameters of the effective configuration of the NbBr₄ molecule are as follows: r_g(Nb?Br)=2.418(5) Å, l(Nb?Br)=0.074(2) Å, r_g(Br?Br)=3.921(16) Å, l(Br?Br)=0.271(12) Å, δ(Br?Br)=0.027(18) Å.     

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.     

Gas-phase electron diffraction and quantum chemical study of the structure of the 4-nitrobenzene sulfonyl chloride molecule

A combined gas-phase electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pVTZ, MP2/6-31G*, and MP2/cc-pVTZ) study of the structure of the 4-nitrobenzene sulfonyl chloride molecule is performed. It is found that at a temperature of 391(3) K only one conformer with C _s symmetry is present in the gas phase. The following experimental values of structural parameters are obtained: r _h1(C-H)_av = 1.086(6) Å, r _h1(C-C)_av = 1.395(3) Å, r _h1(C1-S) = 1.773(4) Å, r _h1(S=O) = 1.423(3) Å, r _h1(S-Cl) = 2.048(4) Å, r _h1(N-O) = 1.224(3) Å, r _h1(N-C4) = 1.477(3) Å, ∠(C1-S=O) = 109.0(4)°, ∠(Cl-S-O) = 106.7(2)°, ∠C1-S-Cl = 100.2(13)°, ∠O=S=O = 122.9(11)°, ∠O=N=O = 123.6(5)°. The C2-C1-S-Cl torsion angle that characterizes the position of the S-Cl bond relative to the benzene ring plane is 89(4)°. The NO₂ group lies in the benzene ring plane. Internal rotation barriers calculated by B3LYP/6-311+G** and MP2/6-31G* methods are: V ₁ = 4.7 kcal/mol and 5.3 kcal/mol for the sulfonyl chloride group; V ₂ = 4.9 kcal/mol and 6.0 kcal/mol for the nitro group.     

Electron diffraction study of the molecular structure of WO2F2

The saturated vapor over solid W ₂ O ₄ F has been studied by electron diffractometry. Structure analysis was fulfilled assuming complex composition of the vapor. It has been established that at T=1043±30 K the vapor consists of WO ₂ F ₂ and WOF ₄ molecules in amounts of 90 and 10 more % respectively. There are two alternative models describing the geometrical structure of the WO ₂ F ₂ molecule (C _2v symmetry) which fit experimental data equally well. In one model, the valence OWO angle is greater than the FWF angle, while in the other, the inverse relation is observed.Ivanovo State University. Moscow Mendeleev Chemical Engineering Institute. Ivanovo Chemical Engineering Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 3, pp. 41–46, May–June 1993.Translated by L. Smolina     

Electron diffraction and quantum-chemical study of the molecular structure of 2-chlorobenzenesulfonyl chloride

The molecular structure of 2-chlorobenzenesulfonyl chloride was studied by electron diffraction and quantum-chemical (2/6-31G**, B3LYP/6-311++G**) methods at 337(3) K. Only one (C ₁) conformer was found in the gas phase. The following structural parameters were obtained: r _h1(C-H)_av = 1.105(6) Å, r _h1(C-C)_av = 1.398(3) Å, r _h1(C-S) = 1.783(11) Å, r _h1(S=O)_av = 1.427(3) Å, r _h1(S-Cl) = 2.048(4) Å, r _h1(C-Cl) = 1.731(9) Å, ∠(C-S=O1) = 109.9(8) °, ∠(C-S=O2) = 106.9(8) °, ∠(Cl1-S-O1) = 107.3(4) °, ∠(Cl1-S-O2) = 106.4(4) ∠, ∠C-S-Cl = 102.1(6) °, ∠O=S=O = 122.3(11) °. The C2-C1-S-Cl1 torsion angle that defines the position of the S-Cl bond relative to the plane of the benzene ring was 69.7(8) °. The B3LYP/6-311++G** calculated barriers of internal rotation of the sulfonyl chloride group were V ₀₁ = 9.7 kcal/mol and V ₀₂ = 3.6 kcal/mol.     

Gas electron diffraction and quantum chemical studies of the molecular structure of 2-nitrobenzenesulfonic acid

A combined gas electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pVTZ) study of the molecular structure of 2-nitrobenzenesulfonic acid (2-NBSA) is performed. Quantum chemical calculations show that the 2-NBSA molecule has five conformers, and the Gibbs energy of one of them is lower by more than 4.5 kcal/mol than the energy of the other conformers. It is found experimentally that the saturated vapor of 2-NBSA at T = 394(5) K contains only the low-energy conformer that has an intramolecular hydrogen bond between the H atom of the hydroxyl group and one of the O atoms of the NO₂ group. The C-C-S-O(H) torsion angle determining the position of the S-O(H) bond is ?72(7)°, while the NO₂ group is substantially turned relative to the benzene ring plane (C1-C2-N-O = 40(5)°). The following experimental values of the internuclear distances are obtained for this conformer (Å): r _h1(C-H)_av = 1.07(2), r _h1(C-C)_av = 1.401(4), r _h1(C-S) = 1.767(6), r _h1(S=O)_av = 1.412(4), r _h1(S-O) = 1.560(6), r _h1(N-O)_av = 1.217(5), r _h1(C-N) = 1.461(8), r _h1(O-H) = 0.99(3).     

Electron diffraction study of the trichloromethyltrichlorogermane molecular structure and estimation for torsional barrier

The molecular geometry (in terms of r_a and r_g internuclear distances) and mean amplitudes of vibration of CCl₃GeCl₃ have been determined by electron diffraction. The bond lengths are similar to those found in analogous molecules. Although bond angles of unambiguous physical definition have not been determined it is established that the carbon and germanium bond configurations deviate little from the regular tetrahedral arrangement. The molecule performs large amplitude motion around the carbon-germanium bond. The torsional barrier was estimated to be 1.1 kcal mole^?1 using J. Karle's method [8].     

Electron diffraction study of the molecular structure and conformation of gaseous 2-furoyl chloride

The molecular structure of 2-furoyl chloride has been investigated by gas-phase electron diffraction at 86°C. Two distinct conformers were identified, a more stable planar form with the furan oxygen and the carbonyl oxygen syn and a less stable planar (or nearly planar) anti form. Assuming that the two forms differ in their geometries only in the O=C---C---O torsion angles and assuming the furan ring to have C_2v symmetry, the results for some of the distances (r_a) and angles (_a) are: r(C---H) = 1.110(20) Å, r(C=O) = 1.207(6) Å, r(C---O) = 1.378(10) Å, r(C??? = 1.465(13) A, (r(C---C)) (average carbon—carbon distance in the furan ring) = 1.392(8) A Δr(C---C) (difference between single and double carbon—carbon distances in the furan ring) = 0.069 A (assumed), r(C---Cl) = 1.787(6) A, C=C---COCl = 131.6(9)°, C=C---O = 110.9(4)°, C=C---H = 127.7(13.4)°, C---C=O = 125.8(8)° and C---C---Cl = 111.8(6)°. At 359 K the observed amount of the conformer with the oxygen atoms syn was 69.8(14.2)%.     

Electron diffraction study of the molecular structure ofo-chloroanisole using a dynamic nonparametrized model

The geometrical parameters of the o-chloroanisole molecule were determined by gas phase electron diffraction in terms of the dynamic model using vibrational spectroscopy data and quantum chemical calculations. A new approach based on Tikhonov's regularization method is used to explicitly define the internal rotation potential of the methoxy group. It was found that the nonparametric internal rotation potential has two minima, one of which corresponds to the planar (?=0°) and another to orthogonal (?=90°) orientation of the O?CH₃ bond relative to the plane of the benzene ring. The difference between the energies of the orthogonal and planar conformers is 0.9–1.0 kcal/mole, and the height of rotation barriers at ??65° is 1.4–1.6 kcal/mole, which confirms the results of quantum chemical calculations, indicating that the orthogonal conformer is present in substantial amounts (～30%). The following basic geometrical parameters were found (r_a in Å, ∠_α in deg, the error equals 3σ): r(C?C)_ave=1.398(4); r(O?C_Ph)=1.358(36); r(O?C_Me)=1.426(21);r(C?Cl)=1.733(4);r(C?H)_Ph=1.086(6);r(C?H)_Me=1.095(6); ∠CC_OC_Cl=118.7(2.2); ∠C_OCC=119.9(2.5); ∠C_OC_ClC=121.5(1.1); ∠COC=117.6(2.6); ∠C_OCCl=119.1(2.1); ∠CCO=124.7(1.2). The results are compared with the data for related compounds. Stereochemical features of o-anisoles that are responsible for the orthogonal conformer are discussed.     

Spectroscopic and quantum chemical study of the structure of 4-aminopyrimidinoanthrones

4-Amino derivatives of pyrimidinoanthrone exist in the form of an aminoketone isomer in the crystalline state in neutral organic solutions, but in acid and alkaline media the tautomeric equilibrium is shifted toward formation of ionic forms of the iminohydroxyl tautomer. We present the characteristics of the IR and electronic absorption spectra and quantum chemical calculations for the neutral and ionic forms of the tautomers indicated above.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1109–1116, August, 1994.     

Molecular structure of magnesium dibromide: an electron diffraction and quantum chemical study

The molecular structure of magnesium dibromide was investigated by high-level computational techniques and gas-phase electron diffraction. The vapor consisted of about 88% monomeric and 12% dimeric species at the electron diffraction experimental conditions at 1065 K. The geometrical parameters and vibrational characteristics of monomeric, dimeric, and trimeric magnesium dibromide species were determined by computations. Very high level computations with extended basis sets and relativistic pseudopotentials on bromine were needed to reach an agreement between computed and estimated experimental equilibrium geometries for the monomer. For both the dimer and the trimer, different geometrical arrangements were tested. Their ground-state structures have halogen bridges with four-membered ring geometries and D2h and D2d symmetry, respectively. Thermodynamic parameters have also been calculated.     

Gas electron diffraction study of the molecular structure of NbCl4

The structure of the NbCl₄ molecule is studied experimentally by the synchronous electron diffraction and mass spectrometry methods. The model molecular geometries of C_2v, C_3v, D_2d, and T_d symmetries are verified. The advantages of the tetrahedral model over the other models are established. The thermally averaged parameters of the effective configuration of the NbCl₄ molecule are as follows: r_g(Nb?Cl)=2.279(5) Å, l(Nb?Cl)=0.073(2) Å, r_g(Cl?Cl)=3.692(17) Å, l(Cl?Cl)=0.275(11) Å, ∠_g(Cl-Nb-Cl)=108.2(5)°, and δ(Cl?Cl)=0.030(19) Å.