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.     

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.     

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.     

Molecular structure and microwave spectra of isotopic chloro-, bromo-, and iodocyanoacetylene

The microwave spectra of the halogeno-cyanoacetylenes, X-CC-CN (X = ¹²⁷I, ⁸¹Br, ⁷⁹Br, ³⁷Cl, ³⁵Cl), have been investigated. The molecules were found to be linear. The vibration-rotation constants of the three bending vibrations and the lower stretching vibration were determined. Lines belonging to the monosubstituted ¹³C and ¹⁵N species in their natural abundances were measured and the rotational constants obtained. The bond distances based on the substitution coordinates were: for I-CC-CN r(I-C) = 1.984₆ Å, r(CC) = 1.207_o Å, r(C-C) = 1.370₂ Å, r(CN) = l.l60₄ Å; for Br-CC-CN, r(Br-C) = 1.785₈ Å, r(CC) = 1.204₁ Å, r(C-C) = 1.369₉ Å, r(CN) = 1.159₃ Å; and for C1-CC-CN, r(Cl-C) = 1.624₅ Å, r(CC) = 1.209_o Å, r(C-C) = 1.369_o Å, r(CN) = 1.160₂ Å.     

The molecular structure of fumaric acid and the deformation of carboxyl group geometry on crystallization

The molecular structure of fumaric acid was studied by means of gas electron diffraction at 260° C. The molecular parameters and their standard deviations obtained for a C_2h model are (r_a distances in Å, angles in degrees): CO: 1.202(0.002), C-O: 1.341(0.006), C-C: 1.486(0.004), CC: 1.356(0.016). C-C-O: 112.1(1.0), C-CO: 124.4(1.1), C-CC: 121.8(1.2). From the available data on carboxylic acids the weighted average deformation of the structure of a carboxylic group on crystallization was determined; a significant expansion of the O-H bond (0.040 Å ), the CO bond (0.010 Å ) and the C-C-O bond angle (1.5° ) and a shrinkage of the C-O bond (0.041 Å ), the C_α-C bond (0.012 Å ) and the C-CO bond angle (2.0° ) was found. The energy for these deformations was estimated to be 1.8 kcal mol^?1.     

An electron diffraction study of 3-methyldiaziridine and 1,2-dimethyldiaziridine

The structures of the title compounds, diaziridines, (the first to be studied in the gas phase) have been determined by electron diffraction. The following principal structural parameters were obtained with the estimated standard deviations parenthesized: 3-methyldiaziridine, N-C = 1.489(9) Å, N-N = 1.444(13) Å, C-C = 1.505(16) Å, C-H = 1.107(5) Å, α =∠ (C-C, NCN) = 61.3° (0.9); 1,2-dimethyldiaziridine, (parameters of the cycle CN₂ were assumed from the previous molecule), N-C (methyl) = 1.445(3) Å, C-H = 1.108(9) Å, ∠ C-N-Me = 112.0° (0.5), the two methyl groups are in the trans position. Vibrational amplitudes were also determined for all important distances.     

An electron diffraction study of the structure of 1,1,2-trichloroethane in the gas phase

The molecular structure of 1,1,2-trichloroethane has been determined by gas phase electron diffraction. The molecule is asymmetric. The geometrical parameters (r_a structure) are: r(C-Cl) 1.776 Å; r(C-H) 0.98 Å; ∠(C-C-Cl) 107°; ∠(Cl-C-Cl) projected along the C-C bond 116°; dihedral angle (Cl-C-C-Cl) 75°. The parameters ∠(C-C-H) 102° and the projected (H-C-H) angle 136° are inaccurate. The structure is rather insensitive to the r(C-C) value, which is unusually long, 1.56 to 1.58 Å.     

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).     

Combined ab initio,electron diffraction,molecular mechanics and vibrational investigations of 1,1 -dimethyl-trans-2-decalone

The conformational behavior of 1,1'dimethyl-trans-2-decalone was studied by combined ab initio, electron diffraction, molecular mechanics and vibrational procedures, and the molecule was found to exist in a distorted all-chair ground state with average C-C, C-H and CO bond distances of r_g = 1.543 Å ± 0.002, r_g = 1.122 Å ± 0.007, and r_g = 1.236 Å ± 0.012, respectively. The ab initio calculations were performed on an STO-3G minimal basis and are indicative of the growing usefulness of quantum-mechanical techniques in the study of medium-sized molecular systems.     

Titan-stickstoff-verbindungen: XIX. Darstellung Und Struktur Des Spirocyclischen Titan-Silylamids Ti(NMeSiMe2MeN)2

deTi(NMeSiMe₂SiMe₂MeN)₂ (I) has been obtained from the reaction of LiNMeSiMe₂SiMe₂NMeLi with TiBr₄. It forms yellow crystals ofconsiderable stability which can be sublimed without decomposition. Its ¹H NMR, IR and Raman spectra are reported. The crystal structure of I was determined by X-ray diffraction and was refined to R = 0.059. The titanium atom in the spiro type molecule is tetrahedrally coordinated by nitrogen atoms with TIN distances of 1.905 Å SiN and SiSi distances in the slightly puckered five-membered rings are 1.733 and 2.355 Å, respectively.     

Structure and conformation of 1,3-dithlane: an electron diffraction study

A gas-phase electron diffraction study of 1,3-dithiane, carried out at 100° C, has found no statistically significant evidence for the presence of any conformer in the vapor other than the chair, within an estimated uncertainty of 10%. An index of the degree of ring puckering in 1,3-dithiane is the average torsional angle which was found to be 61.3°, appreciably greater than that in cyclohexane, but somewhat less than that in 1,4-dithiane and 1,3,5-trithianc. The C-C-C, C-C-S and S-C-S valency angles, 113.6(33)°, 114.9(4)° and 115.0(3)° respectively, were all larger than the C-C-C valency angles in cyclohexane. The C-S-C valency angle, 98.1(7)°, was slightly smaller than that of dimethyl sulfide. Observed bond lengths were r_g(C-H) = 1.116(10) Å, r_g(C-H) = 1.533(5)Å, and r_g(C-S) = 1. 812(3)Å and mean amplitudes of vibration were l_g(C-H) = 0.081(12)Å, l_g(C-C) = 0.052(6)Å and l_g(C-S) = 0.052(4) Å (parenthesized quantities correspond to 3σ). Curiously, nonbonded distances between the axial hydrogen atoms in 1,3-dithiane are virtually identical to those in cyclohexane, even though these molecules have greatly different bond lengths, valency angles, and torsional angles.     

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.     

Reaction between octanetetraone-2,4,5,7 and pentaphenylantimony

Ph₄Sb[OC(Me)CHC(O)(O)CCH(Me)CO]SbPh₄, a binuclear chelate complex, has been synthesized by a reaction between pentaphenylantimony and octanetetraone-2,4,5,7 (2: 1 mol/mol) in toluene. The Sb(1,2) atoms each have a distorted octahedral coordination, the CSbC and CSbO trans-angles lie within a range of 158.3(8)°–169.1(9)°, and the Sb-C bond lengths are 2.06(2)–2.25(2)Å. The two six-membered [SbO₂C₃] chelate rings have the following distances (Å): Sb-O, 2.25(1)–2.29(1); O-C, 1.20(2)–1.32(2); C-C, 1.32(3)–1.53(3).     

The crystal structure of bisphenoxatelluronium dinitrate,C24H16O9N2Te2

Bisphenoxatelluronium dinitrate is monoelinie, P2₁/c: a = 11.638(4), b = 28.266(8), c = 8.546(3) å, β = 119.73(2)°, z = 4 at t = 22°. All atoms including hydrogen were located. The two ring systems, I and II, are folded along their Te-O axes, 147° and 163°, respectively. The average ring bond distances are: Te-C = 2.091, C-C = 1.377, C-O = 1.370 Å. Each Te is bonded to one NO₃ group, Te1-ON1 = 2.485(5), Te2-ON4 = 2.393(4) Å, and an oxygen bridge connects the ring systems, Te1-OB = 1.966(4), Te2-OB = 2.001(4) Å, Te1-OB-Te2 = 125.0(2)°. The bond distances and angles of the structure are compared to those of related compounds.     

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.     

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°.     

X-ray crystal structure of trimethylsilylmethyllithium

The solid state structure of trimethylsilylmethyllithium has been determined by single crystal X-ray diffraction techniques. The compound crystallizes in the monoclinic system, space group P2₁/n. Cell dimensions were determined as follows: a 10.931(3), b 18.397(6), c 21.490(8) Å, β 96.0(2)°, V 4298(2) ų, Z = 4, and a final R_f 5.1% based on 2203 data with σ(I) ≥ 2.5σ(I). The compound is formed by hexameric units, {LiCH₂Si(CH₃)₃}₆, with two distinct classes of LiLi distances of 2.46 and 3.18 Å. There are also two LiC distances av 2.20 and 2.27 Å. The LiH distances to the methylene H atoms have been determined and are short varying between 2.0 and 2.3 Å to the closest lithium atom. The structure, including possible LiH interactions, is discussed and compared with the other known hexameric aggregates.     

Synthesis and crystal structure of (ThCu3)(Mn3+2Mn4+2)O12, a new ferrimagnetic perovskite-like compound

Single crystals of [ThCu₃](Mn³⁺₂Mn⁴⁺₂]O₁₂, a ferrimagnetic perovskite-like compound, have been synthesized by hydrothermal conditions at 600°C and 2 kbar. They have been found to be cubic, of space group Im3, with a = 7.359 Å, and isostructural with [NaMn₃](Mn³⁺₂Mn⁴⁺₂)O₁₂. The crystal structure has been refined by single-crystal X-ray diffraction data. The Th⁴⁺ cations are surrounded by slightly distorted icosahedra; the ThO distance is 2.556 Å. The Cu²⁺ cations are also surrounded by 12 oxygens, which are arranged as three mutually perpendicular rectangles of different size, the smallest and the largest of which are almost squares. The three sets of CuO distances are 1.973, 2.800, and 3.238 Å. The octahedral MnO distance is 1.950 Å. A test based on neutron diffraction powder data indicated that the square sites are occupied by only the Cu²⁺ cations.     

The crystal steueture of phenoxatellurine,C12H8OTe

The crystal structure of phenoxatellurine, C₁₂H₈OTe, was determined by X-ray diffracto-meter methods. The crystals are orthorhorhorhombic, P2₁ 2₁ 2₁, a = 6.036(1), b = 8.160(1), c = 20.717(5) Å at t = 22°. The positions of all atoms, including hydrogen, were found. The central ring is folded along the Te-O axis (138°). Average bond distances are Te-C = 2.098, C-O = 1.397, C-C = 1.382 Å. The phenyl rings are planar with a dihedral angle of 145°; C-Te-C = 89.4(3)°, C-O-C = 121.2(5)°. The structure is compared to those of phenoxathionine and pheuothiazine.     

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°.