An electron diffraction study of the molecular structure of 1,2-difluoroethane

The molecular structure of 1,2-difluoroethane in the gas phase has been determined by electron diffraction at room temperature. Only the gauche conformation was found, the dihedral angle F-C-C-F is 74.5°. The bond lengths r_g(1) are: r(C-C) = 1.535 Å, r(C-F) = 1.394 Å, r(C-H) = 1.13 Å. The valency angles are: α(C-C-F) = 108.3, α(C-C-H) = 108.3. The dihedral angle between the C-C-F and C-C-H planes is 113.6°.     

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°.     

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 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.     

Electron diffraction and quantum-chemical studies of the conformational properties of the 1,3-benzenedisulfochloride molecule

A combined electron diffraction (T = 394(5) K) and quantum-chemical (MP2/6-31G**) study has been performed to investigate the molecular structure of 1,3-benzenedisulfochloride (1,3-BDSC). The 1,3-BDSC molecule was found to exist as the trans (I) and cis (II) stable conformers where the planes containing S-Cl bonds are perpendicular to the plane of the benzene ring. The energy of conformer I is 0.13 kJ/mol lower than that of conformer II. The mutual effect of the sulfochloride groups was found to be absent, which is evident from the coincident bond lengths and angles in the two conformers. The main structural parameters of the conformers are r _h1(C-H)_av = 1.103(4) Å, r _h1(C-C)_av = 1.401(3) Å, r _h1(C-S) = 1.767(4) Å, r _h1(S=O) = 1.422(3) Å, r _h1(S-Cl) = 2.048(4) Å, ∠Cl-S-O = 106.6(2)°, ∠C-S-Cl = 100.4(5)°, ∠ O-S-O = 123.2(5)°.     

The molecular structure of gaseous tetrachloro-p-benzoquinone and tetrachloro-o-benzoquinone by electron diffraction

The structures of tetrachloro-p-benzoquinone and tetrachloro-o-benzoquinone (p- and o-chloranil) have been investigated by gas electron diffraction. The ring distances are slightly larger and the carbonyl bonds slightly smaller than in the corresponding unsubstituted quinones. The molecules are planar to within experimental error, but small deviations from planarity such as those found for the para compound in the crystal are completely compatible with the data. Values for the geometrical parameters (r_a distances and bond angles) and for some of the more important amplitudes (l) with parenthesized uncertainties of 2σ including estimated systematic error and correlation effects are as follows. Tetrachloro-p-benzoquinone: D_2h symmetry (assumed); r(CO) = 1.216 Å(4), r(CC) = 1.353 Å(6), r(C-C) = 1.492 Å(3), r(C-Cl) = 1.701 Å(3), ∠C-C-C = 117.1° (7), ∠CC-C1 = 122.7° (2), l(CO)= 0.037 Å(5), l(CC) = l(C-C) - 0.008 Å(assumed) = 0.049 Å(7), and l(C-Cl) = 0.054 Å(3). Tetrachloro-o-benzoquinone: C_2v symmetry (assumed); r(CO) = 1.205 Å(5), r(CC) = 1.354 Å(9), r(C_cl-C_cl) = 1.478 Å(28), r(Co-C_cl) = 1.483 Å(24), r(C_o-C_o) = 1.526 Å(2), r(C-Cl)= 1.705 Å(3), <C_o-CO = 121.0° (22), ∠C-C-C = 117.2° (9), ∠C_co, ClC-Cl = 118.9° (22), ∠C_ccl, ClC-Cl = 122.2°(12), l(CO) = 0.039 Å(5), and l(C_cl-C_cl) = l(C_o-C_cl) = l( Co-Co) = l(CC) + 0.060 Å(equalities assumed) = 0.055 Å(9). Vibrational'shortenings (shrinkages) of a few of the long non-bond distances have also been measured.     

The molecular structure of 1,1,1-trimethoxyethane in the gas phase as determined by electron diffraction,molecular mechanics calculations and vibratio

The structure of 1,1,1-trimethoxyethane has been studied by electron diffraction in the gas phase. Although this technique cannot discriminate between a GGG (point symmetry C₃) and a TGG (C₁) conformation, vibrational spectra indicate that in the gas phase the C₁ conformer is predominant. Constraints necessary for a satisfactory leastsquares refinement were obtained from molecular mechanics calculations. The molecular geometry as obtained from r_α-refinements is as follows (r_g distances, r_α angles; standard deviations in parentheses): r(C-O central = 1.398 (6) Å, r(C-O)_terminal = 1.431(6)Å, r(C-C) = 1.527 (6) Å, r(C-H) = 1.114 (1) Å, ∠(C-O-C) = 114.0 (4)°, ∠(O-C-H) = 110.7 (4)°; the C-C-O and O-C-0 angles around the central carbon range between 106.6° and 113.1°.     

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.     

The molecular structure of gaseous 2-cyclopentene- 1,4-dione as determined by electron diffraction

The molecular structure of gaseous 2-cyclopentene-1,4-dione has been studied by electron diffraction. The molecule is planar to within the experimental error. The results obtained for some of the more important parameters with estimated uncertainties of 2σ are r(C-H) = 1.093 Å (0.013), r(C0) = 1.208 Å (0.002), r(CC) = 1.341 Å (0.005), r(CH-CO) = 1.493 Å (0.005), r(CO-CH₂) = 1.525 Å (0.005), ∠CC-C = 110.4° (0.3), ∠CH-CO = 124.9° (1.1), ∠CC-H. = 118.7° (5.8), ∠H-C-H = 113.2° (8.7) l(C-H) = 0.0853 A (0.0113), l(CO) = 0.0428 Å (0.0021), l(CC) = 0.0448 Å (0.0037) and l(C-C) = 0.0561 Å (0.0029). The structure is discussed in connection with the structures of related molecules.     

Electron-diffraction study of hydrogen isotope effects in cyclohexane

The electron-diffraction data for cyclohexane and perdeuterated cyclohexane were analyzed and the results were compared. It was found that r_g(C-C) = 1.535 Å (±0.002) for both compounds; r_g (C-H) = 1.116 Å (±0.004) and r_g(C-D) = 1.109 Å (±0.003). Observed hydrogen isotope effects in mean amplitudes agree very well with calculated ones. The C-C bond distance of cyclohexane is in good agreement with some of the previous studies, which is of importance in view of a recent scaling controversy involving this parameter.     

Electron diffraction and quantum chemical study of the molecular structure of 4-methylbenzene sulfochloride

A combined electron diffraction and mass spectrometric study was carried out to investigate the molecular structure of 4-methylbenzene sulfochloride at 330(2) K. An analysis of the electron diffraction data was performed in terms of the r_α structure. Several models of geometrical structure having different orientations of the sulfochloride group relative to the plane of the benzene ring are treated. The following values of structural parameters were obtained: r_α(C-H)_meth= 1.104(41)Å, r_a(C-H)/_phen = 1.103(27)Å, r_a(C-C)_phen = 1.403(7) Å, r_a(C-C)_meth = 1.512(25) Å, r_a(C-S) =1.758(6) Å, r_a(S = O) = 1.419(3) Å,r _a(S-Cl) = 2.049(5) Å, ∠CCH_meth = 106.9(47)?, ∠CSO = 110.5(6)?, ∠CSCl = 101.3(6)°, ∠OSO = 120.5(9)°. The angle between the plane of the benzene ring and the plane of the S-Cl bond was found to be 83°. Ab initio and semiempirical quantum chemical calculations were accomplished to estimate the geometrical and energy parameters and compare them with electron diffraction data.     

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°.     

Structure of gaseous 4-thiacyclohexanone studied by electron diffraction

4-Thiacyclohexanone has been shown to be most stable in the chair conformation. The bond lengths were found to be r_a(CO) = 1.223(5) Å, r_a(C-S) = 1.804(3) Å, r_a(C-C)_av = 1.527(3) Å, r_a(C-H) = 1.116(6) Å. A simple molecular-mechanics calculation agreed with the electron-diffraction results.     

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.     

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°.     

An investigation of the molecular structure of cycloheptanone by gas phase electron diffraction

The electron diffraction data of cycloheptanone, collected at 371 K, can be explained using a model of partial pseudorotation, with the symmetrical twist—chair as the mean structure. Ther_g, r_α-structure is characterized by r(C-C) = 1.536 Å, r(C=O) = 1.219 Å, r(C-H) = 1.124 Å, xxxCC(sp²)C = 117.3°, xxx(CCC = 115.5° and xxx(HCH = 103.2°. Approximate values for the constants of the pseudorotation potential are included.     

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)°.     

Electron diffraction study on the molecular structure of hexamethylcyclotrisilazane, [(CH3)2SiNH]3

A gas electron diffraction study yielded the following geometrical parameters for hexamethylcyclotrisilazane: r(Si-N) = 1.728 ± 0.004 Å, r(Si-C) = 1.871 ± 0.004 Å, r(C-H) = 1.124 ± 0.007 Å, ∠N-Si-N = 108.4 ± 1.0°, ∠Si-N-Si = 126.8 ± 0.8°, ∠C-Si-C = 108.9 ± 2.3°, ∠H-C-H = 111.6 ± 0.9°. The (SiN)₃ ring was found to be puckered but the deviation from planarity is relatively small. Details of the ring shape could not be determined. The degree of ring puckering in six-membered rings with alternating atoms can be roughly predicted from the bond angles in analogous non-cyclic molecules.     

The molecular structure of cyclohexanone determined by gas-phase electron diffraction,including microwave data

The electron diffraction data for gaseous cyclohexanone, collected at 371 K, combined with microwave rotational constants, can be explained by a single chair conformation. Least-squares analysis of the observed data led to an r_g, r_α-structure with the following geometrical parameters: r_CO = 1.229 Å, r_C1C2 = 1.503 Å, r_C1C2 = 1.542 Å, r_C3C4 = 1.545 Å, r_CH = 1.088 Å, ∠ C-CO-C = 115.3°, ∠ CO-C-C = 111.5°, ∠ C-C-C = 110.8°, ∠ H-C-H = 106°. The sp₂ -hybridized part of the ring is less puckered, whereas the sp³ part is more puckered than in cyclohexane.     

The structure of trimethoxymethane in the gas phase,an electron diffraction,ab initio and molecular mechanics study

The structure of trimethoxymethane in the gas phase was studied by electron diffraction, ab initio molecular orbital calculations and molecular mechanics. The molecule was found to exist almost exclusively as an asymmetric all-staggered TGG conformer. The electron diffraction structural parameters (r_g distances, r_α angles) as obtained from geometrically consistent r_α-refinements are: r(C-O) central 1.382(6) Å, r(C-O) terminal 1.418(6) Å, r(C-H) 1.112(1) Å, ∠(O-C-O) in the gauche—gauche chain 115.0(1.0)°, in the gauche-anti chains 109.2(0.6)° ∠(C-O-C) 114.3(0.6)°, ∠(O-C-H)_Me 109.9(0.3)°, methyl torsion 68(6)°. The structure is adequately reproduced by molecular mechanics calculations applying Allinger's force field. The structures of methoxymethanes can be explained in terms of the anomeric effect. This is confirmed by ab initio calculations.