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.     

Gas phase structures of the isomers of benzene,V. (dewar-benzene) by electron diffraction

The parent hydrocarbon, Dewar-benzene, has been studied by gas phase electron diffraction analysis. Assignment of C_2v symmetry gave excellent agreement between the experimental and theoretical data. The structural parameters obtained were in good agreement with previous electron diffraction structures of substituted derivatives of the Dewar-benzene series. The structural parameters with error limits are (cf. Fig. 2): r(C₃-C₆) = 1.574 ± 0.005 Å r(C₂-C₃) = 1.524 ± 0.002 Å, r(C₁-C₂) = 1.345 ± 0.001 Å, r(C₃-C₉) = 1.134 ± 0.004 Å, r(C₁-C₇) = 1.124 ± 0.004 Å, ∠C₁C₆C₅ = 116.7 ± 0.6°, ∠C₃C₆C₁ = 85.7 ± 0.2°, ∠C₆C₃C₉ = 108.0 ± 3.0°, ∠C₃C₂C₈ = 126.7 ± 2.5°, and α = 117.25 ± 0.6°. The angle γ was assumed to be 0°.     

Molecular structure of 1,2,4-triazole

The molecular structure of 1,2,4-triazole has been determined by gas phase electron diffraction. The intemuclear distances and bond angles were obtained by applying a least-squares analysis to the experimental intensity. The bond distances (r_g) and bond angles were N₁-N₂ = 1.380 ± 0.010 Å, N₂C₃ = 1.329 ± 0.009 Å, C₃-N₄ = 1.348 ± 0.009 Å, N₁-C₅ = 1.377 ± 0.004 Å, N₄C₅ = 1.305 Å (calculated value). N-H = 0.990 Å, C-H = 1.054 Å, ∠N₁N₂C₃ = 102.7± 0.5°, ∠N₂C₃N₄ = 113.8 ± 1.3°, ∠N₂N₁C₅ = 108.9 ± 0.8°, ∠H₁N₁N₂ = 110.9°, ∠H₂C₃N₄ = 119.2°, ∠H₃C₅N₁ = 131.0°, ∠C₃N₄C₅ = 105.7° (calculated value) and ∠N₄C₅N₁ = 108.7° (calculated value).     

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 and quantum-chemical studies of the molecular structure of 2-methylbenzenesulfochloride

A combined electron diffraction and quantum-chemical (MP2/6-31G**) study of the molecular structure of 2-methylbenzenesulfochloride at 336(5) K was carried out. It was found that the gas phase contained only one conformer, C ₁. The following structural parameters were obtained: r _h1(C-H)_av = 1.095(8) Å, r _h1(C-C)_Ph = 1.402(4) Å, r _h1(C_Ph-C_meth) = 1.507(13) Å, r _h1(C_Ph-S) = 1.763(6) Å, r _h1(S=O) = 1.418(4) Å, r _h1(S-Cl) = 2.048(5) Å, ∠(H-C-H)_meth/av = 107.3(96)°, ∠(Cl-S-O)_av = 106.4(3)°, ∠C_Ph-S-Cl = 100.8(9), ∠O=S=O = 120.8(10)°. The C_C-C_S-S-Cl torsion angle that defines the position of the S-Cl bond relative to the plane of the benzene ring is 75.6(20)°. The B3LYP/6-311+G** calculated barriers of internal rotation of the methyl and sulfochloride groups are 1.2 kcal/mol and V ₀₁ = 10.2 (V ₀₂ = 4.1) kcal/mol, respectively.     

Electron diffraction and infrared spectroscopic study of the molecular structure of furan-2-aldehyde and 2-furanmethanethiol

Electron diffraction and IR spectroscopic studies of furan-2-aldehyde C₄H₄OCHO and 2-furanmethanethiol C₄H₃OCH₂SH, have been carried out to obtain information on the conformational properties and geometry of these molecules. The electron diffraction data for both molecules were consistent with the assumption that the geometry of the ring skeleton and the hydrogen atoms attached to it were based on the furan structure as determined by microwave spectroscopy. The electron diffraction study ot furan-2-aldehyde confirmed the existence of two conformers with trans and cis oxygen atoms in the ring and aldehyde group. In the gas phase the transconformer was found to be more stable, having less energy by an amount 0.5(4) kcal mol^-1.It was shown that the 2-furanmethanethiol molecule takes a non-planar conformation with dihedral angle O₁C₂C₆S₇ = 39(4)° (0° value of the dihedral angle corresponds to the trans position of the O₁-C₂ and C₆-S₇ bonds, c.f. Fig. 4).The following values were obtained for bond lengths and bond angles characterizing the -CHO and -CH₂SH groups in furan-2-aldehyde and 2-furanmethanethiol molecules, respectively (cf. Figs. 3 and 4)

     

7.

Molecular structure of 1,1-difluoroethylene as determined by gas phase electron diffraction and microwave data     

Frans C. Mijlhoff  Gerrit H. Renes  Kunio Kohata  Kazuko Oyanagi  Kozo Kuchitsu 《Journal of Molecular Structure》1977,39(2):241-252

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.     

8.

The average structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2]oct-2-ene     

Joseph F. Chiang  Raymond L. Chiang  Martin T. Kratus 《Journal of Molecular Structure》1975,26(2):175-188

The average molecular structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2] oct-2-ene have been determined by electron diffraction in the gas phase. The structural parameters were obtained by applying a least squares analysis on the molecular scattering intensity functions. For 2,3-diazabicyclo[2.2.1]hept-2-ene, C_s symmetry was assumed in calculating the geometry of the molecule. The parameters thus determined are: N₃=N₂ = 1.221 Å, N₃- C₄ = 1.445 Å, C₄-C₅ = 1.538 Å, C-H_(ave.) = 1.112 Å, < C₁N₂N₃ = 116.3°, < N₃C₄C₅ = 105.2°, < C₁C₄C₅ = 71.5°, C₄-C₇ = 1.547 Å, C₅-C₆ = 1.530 Å, < C₁C₇C₄ = 108.0°. For 2,3-diazabicyclo[2.2.2]oct-2-ene, C_2vsymmetry was assumed. The geometrical parameters are: N₃ = N₂ = 1.243 Å, N₃-C₄ = 1.473 Å, C₄-C₅ = 1.550 Å, C₅-C₆ = 1.516 Å, C-H_(ave.) = 1.119 Å,< C₁N₂N₃ = 115.1°, < N₃C₄C₅ = 109.1°, < C₆C₁C₄ = 71.6°.     

9.

The structure of 1,2,3,3-tetrachloro-4,5-dimethyl spiro-[2.3] -hexa-1,4-diene     

K.L. Gallaher  S.H. Bauer 《Journal of Molecular Structure》1975,28(1):137-145

An electron diffraction study of 1,2,3,3-tetrachloro-4,5-dimethyl spiro[2.3]-hexa-1,4-diene (Spiro) in the gas phase, confirmed the atom connectivities and led to a structure with roughly tetrahedral bonding about the spiro-carbon atom. The internuclear distances were obtained with moderate precision. The optimum least squares fitting of the experimental molecular scattering function gave a model with C_s symmetry. The r_g values are: (C₃-C₆) = 1.54 (.10) Å (assumed), (C₂-C₃) = 1.52 (.02) Å, <CC >_av= 1.35, (.010) Å, (C₅-C₆) = 1.46 (.02) Å, (C₄-C₇) = 1.52 (.03) Å, (C-Cl) = 1.69 (.03) Å and (-C-Cl) = 1.77 (.03) Å. The angle (θ) between the C₃-C₆ bond and the cyclopropene plane is 127.5°. The large value for <CC >_av is compared with the X-ray crystal structure result, and with the structures of other cyclopropenes and cyclobutenes.     

10.

Internal rotation and equilibrium structure of the 2-methyl-2-nitropropane molecule from joint processing of gas phase electron diffraction data,vibrational and microwave spectroscopy data,and quantum chemical calculation results     

Yu. I. Tarasov  I. V. Kochikov  D. M. Kovtun  E. A. Polenov  A. A. Ivanov 《Journal of Structural Chemistry》2017,58(3):498-507

The structure and internal rotation of the 2-methyl-2-nitropropane molecule is studied by electron diffraction and quantum chemical calculations with the use of microwave and vibrational spectroscopy data. The electron diffraction data are analyzed within the general intramolecular anharmonic force field model and the quantum chemical pseudoconformer model, considering the adiabatic separation of the degree of freedom of large amplitude motion, i.e., the internal rotation of the NO₂ group. The equilibrium eclipsed configuration of the C _s symmetry molecule has the following experimental bond lengths and valence angles: r _e(N=O) = 1.226//1.226(8) Å, r _e(C–N)//r _e(C–C) = 1.520//1.515/1,521(4) Å, ∠_еC–C–N = = 109.1/106,1(8)°, ∠_еO=N=O = 124.2(6)°, ∠_eC–C–H_avg = 110(3)°. The equilibrium geometry parameters are well consistent with MP2/cc-pVTZ quantum chemical calculations and microwave spectroscopy data. The thermally average parameters previously obtained within the small vibration model show a satisfactory agreement with the new results. The electron diffraction data used in this work do not allow a reliable determination of the barrier to internal rotation. However, at a barrier of 203(2) cal/mol, which is derived from the microwave study, it follows from the electron diffraction data that the equilibrium configuration must correspond to an eclipsed arrangement of C–C and N=O bonds, which is also consistent with the results of quantum chemical calculations of various levels.     

11.

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

Ikuo Tokue  Tsutomu Fukuyama  Kozo Kuchitsu 《Journal of Molecular Structure》1974,23(1):33-52

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.     

12.

1,2,4-Triazincs XIII. The bond lengths and bond angles of a 1,2,4-triazine     

J. L. Atwood  D. K. Krass  William W. Paudler 《Journal of heterocyclic chemistry》1974,11(5):743-746

The bond distances and bond angles of 5-(p-chlorophenyl)-1,2,4-triazine determined by three dimensional X-ray crystallographic analysis are reported. The pertinent bond lengths are N₁? N₂, 1.335Å, N₂-C₃, 1.314Å, C₃? N₄, 1.339; N₄-C₅, 1.317; C₅-C₆, 1.401; C₆? N₁, 1.317Å. A comparison of these bond distances with those of similar polyazabenzenes shows that the canonical structure of 1,2,4-triazine with a N₁? N₂ single bond more closely represents the ground state of this ring system, than the one with a N₁? N₂ double bond.     

13.

Synthesis and crystal structure of hexakis(ε-caprolactam)lutetium(III) hexa(isothiocyanato)chromate(III) bis(ε-caprolactam) solvate     

E. V. Cherkasova  E. V. Peresypkina  A. V. Virovets  T. G. Cherkasova 《Russian Journal of Inorganic Chemistry》2016,61(4):447-450

The reaction between Lu(NO₃)₃, K₃[Cr(NCS)₆], and ε-caprolactam (ε-C₆H₁₁NO) in an aqueous solution afforded complex [Lu(ε-C₆H₁₁NO)₆][Cr(NCS)₆] · 2(ε-C₆H₁₁NO) (I), the structure of which was determined by IR spectroscopy and X-ray diffraction. Crystals of I are triclinic, space group \(P\bar 1\), Z = 1, a = 12.1371(7) Å, b = 12.2082(7) Å, c = 12.7090(7) Å, α = 67.2920(10)°, β = 87.9130(10)°, γ = 82.9410(10)°, V = 1723.86(17) ų, ρ_calc = 1.426 g/cm³.     

14.

Molecular structure of carbonyl bromide as studied by gas electron diffraction     

Munetaka Nakata  Tsutomu Fukuyama  C.J. Wilkins  Kozo Kuchitsu 《Journal of Molecular Structure》1981

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.     

15.

Crystal and molecular structure of (hexafluoroacetylacetonato) (pivaloylacetonato)copper(II)     

I. A. Baidina  S. A. Gromilov  A. D. Vasilyev 《Journal of Structural Chemistry》2005,46(1):177-181

The crystal structure of (hexafluoroacetylacetonato)(pivaloylacetonato)copper(II) has been determined. Crystal data for CuO₄C₁₃H₁₄F₆: a = 8.288(2) Å, b = 8.682(2) Å, c = 12.307(2) Å; α = 90.75(3)°, β = 94.29(3)°, γ = 106.60(3)°; V = 845.7(3) ų, space group \(P\overline 1 \), Z = 2, d_calc = 1.617 g/cm³. The coordination polyhedron of the copper atom is formed by four oxygen atoms of two different β-diketonate ligands with Cu-O distances within 1.874–1.946 Å; the O-Cu-O bond angles are 94.8° and 90.6°. The complexes are united into centrosymmetrical “dimers” with Cu...Cu distances of 4.365 Å.     

16.

An electron diffraction study of the molecular geometry of dimethyl sulphone     

Magdolna Hargittai  István Hargittai 《Journal of Molecular Structure》1974,20(2):283-292

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.     

17.

The structure of cyclopentene oxide determined by gas phase electron diffraction     

R.L. Hilderbrandt  J.D. Wieser 《Journal of Molecular Structure》1974,22(2):247-255

The r_g structure of cyclopentene oxide has been determined by the simultaneous least squares analysis of electron diffraction and microwave spectroscopic data. The investigation has reaffirmed previous studies indicating that the molecule prefers a boat conformation. The methylene and epoxide flap angles obtained are 152.3±2.1° and 104.7±1.0° respectively. Other structural parameters determined are: r_g (C-H avg.) = 1.120±0.004 Å; r_g (C-C avg.) = 1.538±0.002 Å; r_g (C-O) = 1.443±0.003 Å, and r_g (C-C) = 1.482±0.004 Å for the carbon-carbon bond in the three membered epoxide ring. These results compare favorably with the reported structures of ethylene oxide and cyclohexene oxide. A tentative rationalization of the unusual boat conformation is also offered.     

18.

On the molecular structure of (CH₃)₂NSO₂N(CH₃)₂ as studied by gas electron diffraction     

István Hargittai  Erzsébet Vajda  Annamária Szöke 《Journal of Molecular Structure》1973,18(3):381-390

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.     

19.

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

V. Mom  P.A.G. Huisman  F.C. Mijlhoff  G.H. Renes 《Journal of Molecular Structure》1980

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).     

20.

A gas-phase electron diffraction study of the molecular structure of tetravinylsilane     

S. Rustad  B. Beagley 《Journal of Molecular Structure》1978,48(3):381-388

The molecular structure of tetravinylsilane has been studied by gas-phase electron diffraction. The radial distribution curve suggests the absence of conformers having vinyl double bonds staggered with respect to the SiC₄ skeleton. Of the eclipsed or approximately-eclipsed conformers, the one with S₄ symmetry gives the best fit with experiment, although a small admixture of a C₁ conformation cannot be ruled out. Least-squares refinement gave the following values for the independent structural parameters (lengths, r_a basis; angles, r_α basis): C-H = 1.118 ± 0.003 Å, CC = 1.355 ± 0.002 Å, Si-C = 1.855 ±0.002 Å, ∠SiCC = 124.0 ± 0.3°, ∠SiCH = 118.4 ± 1.0°, torsion angles CSiCC are 17.5 ± 0.6° from the eclipsed conformation. During the refinement the vibrational amplitudes u and perpendicular amplitude corrections K were held constant at calculated values. The CC bond length provides evidence of interaction between the vinyl π-bonds and the vacant d-orbitals of silicon.     

C4H3OCHO	C4H3OCH2SH
ra(C2-C6) = 1.453(7) Å	ra(C2-C6) = 1.481(15) Å
ra(C6O7) = 1.212(4)Å	ra(C2-S7) = 1.834(5) Å
∠O1C2C5 =117.6(4)°	ra(C6-H) = 1.106(17) Å
∠C2C6O7 = 122.7(8)°	∠O1C2C6 = 114.4(11)°	∠C2C6S4 = 112.5(8)°

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.     

The average structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2]oct-2-ene

The average molecular structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2] oct-2-ene have been determined by electron diffraction in the gas phase. The structural parameters were obtained by applying a least squares analysis on the molecular scattering intensity functions. For 2,3-diazabicyclo[2.2.1]hept-2-ene, C_s symmetry was assumed in calculating the geometry of the molecule. The parameters thus determined are: N₃=N₂ = 1.221 Å, N₃- C₄ = 1.445 Å, C₄-C₅ = 1.538 Å, C-H_(ave.) = 1.112 Å, < C₁N₂N₃ = 116.3°, < N₃C₄C₅ = 105.2°, < C₁C₄C₅ = 71.5°, C₄-C₇ = 1.547 Å, C₅-C₆ = 1.530 Å, < C₁C₇C₄ = 108.0°. For 2,3-diazabicyclo[2.2.2]oct-2-ene, C_2vsymmetry was assumed. The geometrical parameters are: N₃ = N₂ = 1.243 Å, N₃-C₄ = 1.473 Å, C₄-C₅ = 1.550 Å, C₅-C₆ = 1.516 Å, C-H_(ave.) = 1.119 Å,< C₁N₂N₃ = 115.1°, < N₃C₄C₅ = 109.1°, < C₆C₁C₄ = 71.6°.     

The structure of 1,2,3,3-tetrachloro-4,5-dimethyl spiro-[2.3] -hexa-1,4-diene

An electron diffraction study of 1,2,3,3-tetrachloro-4,5-dimethyl spiro[2.3]-hexa-1,4-diene (Spiro) in the gas phase, confirmed the atom connectivities and led to a structure with roughly tetrahedral bonding about the spiro-carbon atom. The internuclear distances were obtained with moderate precision. The optimum least squares fitting of the experimental molecular scattering function gave a model with C_s symmetry. The r_g values are: (C₃-C₆) = 1.54 (.10) Å (assumed), (C₂-C₃) = 1.52 (.02) Å, <CC >_av= 1.35, (.010) Å, (C₅-C₆) = 1.46 (.02) Å, (C₄-C₇) = 1.52 (.03) Å, (C-Cl) = 1.69 (.03) Å and (-C-Cl) = 1.77 (.03) Å. The angle (θ) between the C₃-C₆ bond and the cyclopropene plane is 127.5°. The large value for <CC >_av is compared with the X-ray crystal structure result, and with the structures of other cyclopropenes and cyclobutenes.     

Internal rotation and equilibrium structure of the 2-methyl-2-nitropropane molecule from joint processing of gas phase electron diffraction data,vibrational and microwave spectroscopy data,and quantum chemical calculation results

The structure and internal rotation of the 2-methyl-2-nitropropane molecule is studied by electron diffraction and quantum chemical calculations with the use of microwave and vibrational spectroscopy data. The electron diffraction data are analyzed within the general intramolecular anharmonic force field model and the quantum chemical pseudoconformer model, considering the adiabatic separation of the degree of freedom of large amplitude motion, i.e., the internal rotation of the NO₂ group. The equilibrium eclipsed configuration of the C _s symmetry molecule has the following experimental bond lengths and valence angles: r _e(N=O) = 1.226//1.226(8) Å, r _e(C–N)//r _e(C–C) = 1.520//1.515/1,521(4) Å, ∠_еC–C–N = = 109.1/106,1(8)°, ∠_еO=N=O = 124.2(6)°, ∠_eC–C–H_avg = 110(3)°. The equilibrium geometry parameters are well consistent with MP2/cc-pVTZ quantum chemical calculations and microwave spectroscopy data. The thermally average parameters previously obtained within the small vibration model show a satisfactory agreement with the new results. The electron diffraction data used in this work do not allow a reliable determination of the barrier to internal rotation. However, at a barrier of 203(2) cal/mol, which is derived from the microwave study, it follows from the electron diffraction data that the equilibrium configuration must correspond to an eclipsed arrangement of C–C and N=O bonds, which is also consistent with the results of quantum chemical calculations of various levels.     

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.     

1,2,4-Triazincs XIII. The bond lengths and bond angles of a 1,2,4-triazine

The bond distances and bond angles of 5-(p-chlorophenyl)-1,2,4-triazine determined by three dimensional X-ray crystallographic analysis are reported. The pertinent bond lengths are N₁? N₂, 1.335Å, N₂-C₃, 1.314Å, C₃? N₄, 1.339; N₄-C₅, 1.317; C₅-C₆, 1.401; C₆? N₁, 1.317Å. A comparison of these bond distances with those of similar polyazabenzenes shows that the canonical structure of 1,2,4-triazine with a N₁? N₂ single bond more closely represents the ground state of this ring system, than the one with a N₁? N₂ double bond.     

Synthesis and crystal structure of hexakis(ε-caprolactam)lutetium(III) hexa(isothiocyanato)chromate(III) bis(ε-caprolactam) solvate

The reaction between Lu(NO₃)₃, K₃[Cr(NCS)₆], and ε-caprolactam (ε-C₆H₁₁NO) in an aqueous solution afforded complex [Lu(ε-C₆H₁₁NO)₆][Cr(NCS)₆] · 2(ε-C₆H₁₁NO) (I), the structure of which was determined by IR spectroscopy and X-ray diffraction. Crystals of I are triclinic, space group \(P\bar 1\), Z = 1, a = 12.1371(7) Å, b = 12.2082(7) Å, c = 12.7090(7) Å, α = 67.2920(10)°, β = 87.9130(10)°, γ = 82.9410(10)°, V = 1723.86(17) ų, ρ_calc = 1.426 g/cm³.     

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.     

Crystal and molecular structure of (hexafluoroacetylacetonato) (pivaloylacetonato)copper(II)

The crystal structure of (hexafluoroacetylacetonato)(pivaloylacetonato)copper(II) has been determined. Crystal data for CuO₄C₁₃H₁₄F₆: a = 8.288(2) Å, b = 8.682(2) Å, c = 12.307(2) Å; α = 90.75(3)°, β = 94.29(3)°, γ = 106.60(3)°; V = 845.7(3) ų, space group \(P\overline 1 \), Z = 2, d_calc = 1.617 g/cm³. The coordination polyhedron of the copper atom is formed by four oxygen atoms of two different β-diketonate ligands with Cu-O distances within 1.874–1.946 Å; the O-Cu-O bond angles are 94.8° and 90.6°. The complexes are united into centrosymmetrical “dimers” with Cu...Cu distances of 4.365 Å.     

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.     

The structure of cyclopentene oxide determined by gas phase electron diffraction

The r_g structure of cyclopentene oxide has been determined by the simultaneous least squares analysis of electron diffraction and microwave spectroscopic data. The investigation has reaffirmed previous studies indicating that the molecule prefers a boat conformation. The methylene and epoxide flap angles obtained are 152.3±2.1° and 104.7±1.0° respectively. Other structural parameters determined are: r_g (C-H avg.) = 1.120±0.004 Å; r_g (C-C avg.) = 1.538±0.002 Å; r_g (C-O) = 1.443±0.003 Å, and r_g (C-C) = 1.482±0.004 Å for the carbon-carbon bond in the three membered epoxide ring. These results compare favorably with the reported structures of ethylene oxide and cyclohexene oxide. A tentative rationalization of the unusual boat conformation is also offered.     

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.     

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).     

A gas-phase electron diffraction study of the molecular structure of tetravinylsilane

The molecular structure of tetravinylsilane has been studied by gas-phase electron diffraction. The radial distribution curve suggests the absence of conformers having vinyl double bonds staggered with respect to the SiC₄ skeleton. Of the eclipsed or approximately-eclipsed conformers, the one with S₄ symmetry gives the best fit with experiment, although a small admixture of a C₁ conformation cannot be ruled out. Least-squares refinement gave the following values for the independent structural parameters (lengths, r_a basis; angles, r_α basis): C-H = 1.118 ± 0.003 Å, CC = 1.355 ± 0.002 Å, Si-C = 1.855 ±0.002 Å, ∠SiCC = 124.0 ± 0.3°, ∠SiCH = 118.4 ± 1.0°, torsion angles CSiCC are 17.5 ± 0.6° from the eclipsed conformation. During the refinement the vibrational amplitudes u and perpendicular amplitude corrections K were held constant at calculated values. The CC bond length provides evidence of interaction between the vinyl π-bonds and the vacant d-orbitals of silicon.