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.     

Molecular structure of hexafluorobicyclo [2.2.0]hexa-2,5-diene (hexafluoro-dewar-benzene) in the vapour phase

Hexafluoro-Dewar-benzene has been studied by the electron-diffraction method. A model with C_2v symmetry gives excellent agreement between experimental and theoretical data. The structural parameters with error limits are (cf. Fig. 1): r(C₁-C₄)= 1.598 ±0.017 Å, r(C₁-C₂) = 1.505 ±0.005 Å, r(C₂-C₃) = 1.366 ± 0.015 Å, r(C₁-F₁) = 1.328±0.015 Å, r(C₂-F₂) = 1.319±0.007 Å, ∠F₁C₁C₄ = 118.7±0.7°, ∠F₂C₂C₃ = 133.6±0.7°, τ= 121.8±2.0°, and δ = -7.5±2.0°. Molecular orbital calculations by the CNDO/2 method gave τ = 119.8° and δ = ?4.2°.     

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°.     

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.     

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.     

An electron diffraction investigation of the molecular structure of dichloromaleic anhydride

The molecular structure of gaseous dichloromaleic anhydride has been investigated by electron diffraction at a nozzle-tip temperature of 164–170°C. The molecule is planar to within experimental error, but small deviations from planarity corresponding to torsion up to about 10° around the carbon-carbon single bonds cannot be ruled out. Values of the more important r_α distances and angles with estimated 2σ uncertainties are r(CO) = 1.188(2) Å, r(CC) = 1.332(5) Å, r(C-O) = 1.389(3) Å, r(C—C) = 1.495(3) Å, r(C—Cl) = 1.685(2) Å, ∠CC-Cl = 129.4(2)°, ∠C-CO = 128.5(4)° and ∠CC—C = 107.9(2)°. The shortening of the carbonyl bond relative to that in maleic anhydride itself is discussed in terms of a possible general effect of vicinal substitution.     

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.     

Molecular structure and conformation of gaseous bromoacetyl chloride and bromoacetyl bromide as determined by electron diffraction

Bromoacetyl chloride and bromoacetyl bromide are studied by gas phase electron diffraction at nozzle-tip temperatures of 70°C and 77°C, respectively. Both compounds exist as mixtures of anti and gauche conformers. The mole fraction anti, with uncertainties estimated at 2σ, was found to be 0.474(0.080) for bromoacetyl chloride and 0.615(0.069) for bromoacetyl bromide. The results for the distance (r_a)and angle (∠α) parameters, with parenthesized uncertainties of 2σ including estimated uncertainty in the electron wave length and correlation effects are as follows: (1) bromoacetyl chloride, r(C-H) = 1.086(0.062) Å, r(CO) = 1.188(0.009) Å, r(C-C) = 1.519(0.018) Å, r(C-Cl) = 1.789(0.011) Å, r(C-Br) = 1.935(0.012) Å, ∠C-CO = 127.6(1.3)°, ∠C-C-Cl = 111.3(1.1)°, ∠C-C-Br = 111.0(1.5)°, ∠H-C-H = 109.5°(assumed), $\text{}\text{?}$/o (gauche torsion angle relative to 0° for the anti form) = 110.0°(assumed); (2) bromoacetyl bromide, r(C-H) =1.110(0.088) Å, r(C=O) = 1.175(0.013) Å, r(C-C) = 1.513(0.020) Å, r(CO-Br) = 1.987(0.020) Å, r(CH₂-Br) = 1.915(0.020) Å, ∠C-CO = 129.4(1.7)°, ∠CH₂-CO-Br = 110.7(1.5)°, ∠CO-CH₂-Br = 111.7(1.8)°, ∠H-C-H = 109.5°(assumed), ∠ø (gauche torsion angle relative to 0° for the anti form) = 105.0°(assumed). The structural results are discussed in connection with the structures of related molecules.     

Molecular structure and conformation of gaseous 2-chloro-3-fluoro-1-propene

2-Chloro-3-fluoro-1-propene has been studied by electron diffraction, and the molecule was found to exist in equilibrium between a syn and a gauche conformation, with the syn conformation as the most stable. The most important structure parameters with standard deviation are: r_g(CC) = 1.338(6) Å,r_g(C—C) = 1.505(5) Å, r_g(C—F) = 1.378(4) Å, r_g(C-Cl) = 1.743(3) Å, ∠CC—Cl = 123.0(7)°, ∠CC—C = 125.6(6)° and ∠C—C—F = 111.2(8)°.A force field was determined by a least-squares refinement to vibrational frequencies. Mean square amplitudes of vibration and perpendicular amplitude correction coefficients have been calculated. The mean square amplitudes of vibration from the electron diffraction data are in very good agreement with the values calculated from the spectroscopic data.     

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.     

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.     

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°.     

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.     

Electron diffraction and CNDO/2 investigation on the molecular structure of tetrafluoro-1,3-diselenetane (F2CSe)2

The molecular structure of tetrafluoro-1,3-diselenetane was determined in the gas phase by electron diffraction. A planar ring configuration with the following geometric parameters (r_g-values) was obtained:r(Se-C) = 1.968 ± 0.004 Å, r(C-F) = 1.353 ± 0.003 Å, ∠SeCSe = 98.5° ± 0.4°, ∠FCF = 106.3 ± 0.8°. SCF-MO calculations in the CNDO/2 approximation confirm the planarity of the four membered ring and give a plausible explanation for the remarkably short Se-C bond length in the ring which in spite of ring strain is shorter than in Se(CF₃)₂. There exists a strong bonding interaction between the diagonal selenium atoms which amounts to about one fourth of a normal single bond strength.     

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.     

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 conformation of gaseous chloroacetyl chloride as determined by electron diffraction

Chloroacetyl chloride is studied by gas-phase electron diffraction at nozzle-tip tempera- tures of 18, 110 and 215°C. The molecules exist as a mixture of anti and gauche confor- mers with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ is found to be 0.770 (0.070), 0.673 (0.086) and 0.572 (0.086) at 18, 110 and 215°C, respectively. These values correspond to an energy difference with estimated standard deviation ΔE^o = E^o_g -E^o_a = 1.3 ± 0.4 kcal mol^?1 and an entropy difference ΔS^o = S^o_g -S^o_a = 0.7 ± 1.1 cal mol^?1 K^?1. Certain of the diffraction results permit the evaluation of an approximate torsional potential function of the form 2V = V₁(1 - cos φ) + V₂(1 - cos 2φ) + V₃(1 - cos 3φ); the results are V₁ = 1.19 ± 0.33, V₂ = 0.56 ± 0.20 and V₃ = 0.94 ± 0.12, all in kcal mol^?1. The results for the distance (r_a), angle (_∠α) and r.m.s. amplitude parameters obtained at the three temperatures are entirely consistent. At 18°C the more important parameters are, with estimated uncertainties of 2σ, r(C-H) = 1.062(0.030) Å, r(CO) = 1.182(0.004) Å, r(C-C) = 1.521(0.009) Å. r(CO-Cl) = 1.772(0.016) Å, r(CH₂-Cl) = 1.782(0.018) Å, ∠C-C-0 = 126.9(0.9)°, ∠CH₂-CO-C1 = 110.0(0.7)°,∠CO-CH₂-C1 = 112.9(1–7)°, ∠H-C-H = 109.5° (assumed), ∠φ (gauche torsion angle relative to 0° for the anti form) = 116.4(7.7)°, δ (r.m.s. amplitude of torsional vibration in the anti conformer) == 17.5(4.2)°.     

Electron diffraction study and CNDO/2 calculations on the complex of aluminium trichloride with ammonia,Cl3Al.NH3

The molecular geometry of the complex of aluminium trichloride with ammonia, Cl₃Al.NH₃, has been studied by electron diffraction. The most important internuclear distances in terms of r_a parameters are as follows: r(Al-Cl) = 2.100±0.005 Å, r(Al-N) = 1.996±0.019 Å, r(Cl·Cl) = 3.569±0.011 Å and r(Cl·N) = 3.165±0.012 Å. The Cl-Al-Cl bond angle in terms of an approximate r_a structure is 116.9°. The assumptions of a staggered model in the structure analysis was justified by CNDO/2 calculations. The experimental data indicate strong linkage between the donor and acceptor parts. The flat pyramidal average configuration of the AlCl₃ part of the complex suggests planar equilibrium structure for free AlCl₃. Variations in the bond configurations of the donor and acceptor parts, as compared with those of the respective free molecules, 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).