The conformational behaviour of divinyl ether in the gas phase was explored by infrared band profile simulations and joint analysis of electron diffraction and microwave data. At 300 K the rotameric mixture contains 80% [sp, ac] and 20% [ap, ap] forms. Geometries have been studied using constraints taken from ab initio 4-21G gradient geometry and force field calculations. Differences between some unresolved bond distances and angles were constrained to the calculated values. Scale factors for the ab initio force field were refined from the diffraction data. In addition the transferability of scale factors from methyl vinyl ether to divinyl ether was tested. The investigation demonstrates that molecular orbital constrained models are consistent with and rationalize all experimental gas phase results. Subject to the ab initio constraints, the analysis yields the following model (rg-distances, r-angles; numbers in parentheses are 6 times the least-squares ESDs): (C---H) = 1.103(12) A, (C---C) = 1.337(2) A, (C---O) = 1.389(2) A. Torsion angles for the [sp, ac] form are −13(6)° and 145(4)°. 相似文献
Gaseous bis(hexamethydisilylamido)mercury(II), Hg{N(SiMe3)2)2}2, has been studied by electron diffraction at a nozzle temperature of ca 390 K.
The diffraction data are consistent with a model consisting only of monomers. By assuming the NHgN chain to be linear and the HgHSi2 fragments to be planar, an equilibrium conformer with a staggered Si2NHgNSi2 skeleton of Dad-symmetry may be brought into a nice agreement with the observed diffraction data. The relatively large value of the vibrational amplitude of the inter-ligand SiSi distance, 0.26(12) A, indicates that the ligands undergo large amplitude vibrations about the NHgN axis. Steric considerations as well as the magnitude of the rotational barrier as estimated from the diffraction data (ca. 2 kcal mol−1) show that this motion is hindered. A model with an eclipsed, co-planar Si2NHgNSi2 backbone of Dadsymmetry could not satisfactorily be brought into agreement with the observed diffraction data.
The values of some relevant key-parameters are: ra(Hg---N) = 2.01(2) A, ra(Si---N) = 1.732(9) A, ra(Si---C) = 1.883(6) A;HgNSi = 116.0(1.0)°, SiNSi = 128.0(2.0)°, NSiC= 111.8(1.2)° and SiCH = 111.0(2.0)°. The trimethylsilyl groups are twisted 25(3)° away from their references positions typified by one Si---C bond of each such group eclipsing the adjacent Hg---N bond, in such a way that the overall symmetry of the model is lowered from Dad to S4. 相似文献
The potential function for internal rotation of the aldehyde group in the orthometa- and para-fluorobenzaldehydes is calculated by CNDO/2, INDO and STO/6G methods, assuming invariant bond lengths. The INDO and STO/6G calculations indicate the equilibrium geometry to be essentially planar and the barrier to internal rotation to be the potential energy of the molecule when the plane of the aldehyde group is perpendicular to the ring plane; CNDO/2 leads to different conclusions, however. Relative stabilities of O-cis and O-trans rotamers of the planar configuration are discussed. Comparisons are made with the V barriers and the enthalpies of activation as determined by the dielectric absorption method using a matrix technique. 相似文献
The performance of the VN—1 potential model at the INDO/2 level of approximation in the calculation of transition energy, singlet—triplet splitting, change in molecular structure, inversion barrier and electron-density distribution in the excited electronic states of a few simple carbonyls is analysed. The method turns out to be reasonably successful in many ways. 相似文献
The molecular structure of norbornene has been investigated in the gas phase by combining electron diffraction data with microwave spectroscopic rotational constants. The interatomic distances (rg) and bond angles were obtained by applying a least squares program to the refined experimental molecular diffraction intensities. The CC bond length was found to be 1.336 ± 0.002 Å while the ) bond length was 1. 529 ± 0.007 Å. Other bond lengths and angles included (IUPAC numbering system was used for norbornene): C1-C6 = 1.550 ± 0.020 Å, C1-C7 = 1.566± 0.005 Å, C5-C6 = 1.556 ± 0.005 Å, C-Have. = 1.103 ± 0.003 Å, ∠C1C2C4 = 95.3°. The dihedral angle between planes C1C2C3C4 and C1C6C5C4 is 110.8 ± 1.5° while that between C1C2C3C4 and C1C7C4 is 122.3°. The moments of inertia calculated from ED structure are in good agreement with microwave spectroscopic values. 相似文献
The molecular structure of carbonyl fluoride has been determined by electron diffraction. The results have been used in conjunction with the rotational constants reported by Carpenter in a combined structure analysis. The values so obtained are rz (C=O) = 1.1717 ± 0.0013 Å, rz (C-F) = 1.3157 ± 0.0005 Å, and ∠zF-C-F = 107.71 ± 0.08°. These agree with the corresponding parameters estimated by Carpenter from the rotational constants alone. The effective constants, α3, representing the cubic anharmonicity of bond stretching vibrations have been estimated. 相似文献
The structure of the paraelectric phase of RbHSeO4 has been determined at 387 K by neutron diffraction. The structure consists of chains of hydrogen bonded SeO4 groups extending along the crystallographic b axis. Two different hydrogen bonds have been characterized, with OO distances of 2.524(4) and 2.583(3) Å. In the shorter OHO hydrogen bond the hydrogen atom is disordered, suggesting that the ordering of hydrogen participates directly in the phase transition to the ferroelectric phase. 相似文献
Atomic hyperfine structures were measured for the Cu I transition at 5782 A by optogalvanic spectroscopy at high resolution, with a cw dye laser. Samples were electro-deposited on the demountable cathode of a home-made hollow-cathode lamp. By spectral deconvolution, the relative isotopic abundances of (63)Cu and (65)Cu could be determined with good accuracy and precision. The technique is applicable to copper concentrations as low as 1.6 ppm. 相似文献
The molecular structure of allyl silane has been studied by gas-phase electron diffraction. The experimental radial distribution curve has only four prominent peaks, resulting in serious resolution problems in the structure determination. A single conformer whose dimensions resemble those of related molecules fits the diffraction data. The torsion angle φsiccc is102 ± 1°, measured from the conformation having Si-C and CC eclipsed. 相似文献
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 (rg = 1.122±0.006 Å) was substantially longer than the average methyl C-H distance (rg = 1.113±0.002 Å). Other structural parameters obtained were: rg(C-C) = 1.535±0.001 Å, ∠CCC = 110.8±0.2°, and the average ∠CCH (methyl) = 111.4±0.2°. 相似文献
A flame atomic-absorption spectroscopy method for determination of nickel in the serum of occupationally exposed subjects has been developed. Trichloroacetic add is utilized for precipitating proteins and freeing bound nickel; sodium diethyldithiocarbamate is used as complexing agent and isopropyl acetate as the solvent for extraction. The method is characterized by good accuracy, precision and sensitivity, over a concentration range up to about 20 ng/ml. Calcium, which is present in serum in great excess with respect to typical nickel concentrations, does not interfere in the determination of the latter. 相似文献
The history of the interaction between experimental structure determinations by microwave spectroscopy and by gas phase electron diffraction is briefly reviewed in terms of three eras: (1) competition and antagonism, (2) comparison and correction, and (3) integration of analysis. A similar progression is noted for the relation between experimental and theoretical methods for studying molecular structure, with the present time straddling ages (2) and (3). Examples are given from a variety of studies involving various degrees of methodological interaction. The true integration of experimental and computational structural studies is still in its infancy with the primary illustrations involving the evaluation of theoretical structural offset values from experimental evidence, the transfer of theoretically determined parameters into the fitting of experimental data, and the current development of methods for utilizing vibrational information obtained from the combined analysis of computed theoretical and experimental infrared data in the further analysis of experimental diffraction and microwave information. 相似文献
The electronic structure of N,N-dimethylnitranine. (CH3)2NNO2, and N,N,-dimethylnitrosamine, (CH3)2NNO, has been investigated through the use of electron spectroscopy and quantum chemical methods. Experimentally, the electron spectra of (CH3)2NNO2 and (CH3)2NNO were measured in the valence region on the gas phase molecules using UV (HeI and He II) radiation and in the valence and core regions on the solid materials (frozen at 170 K) using X-radiation (AlKα). Theoretically, the results of INDO and MWH Extended Hucket MO calculations are used for spectral interpretation. The semi-empirical potential model of Ellison is used for predicting is chemical shifts. The results of this investigation exemplify how the UV and X-ray electron spectroscopy techniques are symbiotic and how application of the two techniques along with the use of quantum chemical methods provide unique information about electronic structures. 相似文献
The structure of methyl formate in the gas phase has been reinvestigated by electron diffraction. The results confirm that the molecular skeleton is cis-planar, with bond lengths and angles in close agreement with those found by microwave techniques. Principal parameters (ra) are: r(CO) 120.2(2) pm, r(C-O) 134.0(2), and 143.5(3) pm; ∠ (OC-O) 125.4(5)°, and ∠ (C-O-C) 115.9(5)°. 相似文献
Pure crystalline samples of HTaO3 and DTaO3 have been prepared. The crystal structure has been solved using powder X-ray and neutron diffraction (at 2 K and room temperature) and has been shown to consist of Ta(O,OH)6 octahedra sharing vertices with the oxygen atoms displaced toward the vacant perovskite A sites. The compound is isomorphous with HNbO3, DxWO3, and DxReO3 and contains hydrogen atoms as hydroxide groups. 相似文献
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 (ra 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: D2h symmetry (assumed); r(CO) = 1.216 Å(4), r(CC) = 1.353 Å(6), r(C-C) = 1.492 Å(3), r(C-Cl) = 1.701 Å(3), ∠C-C-C = 117.1° (7), ∠CC-C1 = 122.7° (2), l(CO)= 0.037 Å(5), l(CC) = l(C-C) - 0.008 Å(assumed) = 0.049 Å(7), and l(C-Cl) = 0.054 Å(3). Tetrachloro-o-benzoquinone: C2v symmetry (assumed); r(CO) = 1.205 Å(5), r(CC) = 1.354 Å(9), r(Ccl-Ccl) = 1.478 Å(28), r(Co-Ccl) = 1.483 Å(24), r(Co-Co) = 1.526 Å(2), r(C-Cl)= 1.705 Å(3), <Co-CO = 121.0° (22), ∠C-C-C = 117.2° (9), ∠Cco, ClC-Cl = 118.9° (22), ∠Cccl, ClC-Cl = 122.2°(12), l(CO) = 0.039 Å(5), and l(Ccl-Ccl) = l(Co-Ccl) = l( Co-Co) = l(CC) + 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. 相似文献
The molecular geometry of selenium oxychloride has been studied by electron diffraction. The internuclear distances (in terms of ra) are: r(Se-O) 1.612 ± 0.005 Å, r(Se-Cl) 2.204 ± 0.005 Å, r(Cl β O) 3.064 ± 0.012 Å, r(Cl β Cl) 3.295 ± 0.016 Å. The bond angles are ∠Cl-Se-O 105.8 ± 0.7° and ∠ Cl-Se-Cl 96.8 ± 0.7°. The structural parameters of three simple selenium-oxygen compounds are compared with those of their sulphur analogs in terms of the valence shell electron pair repulsion model. 相似文献
The IR and Raman spectra of methyl-d3 vinyl and methyl-d3 vinyl-d3 ethers are reported (along with earlier published spectra of the undeuterated molecule). The normal coordinate analysis, based upon CNDO/2 force constant calculations, confirms the absence of significant changes in CH3 group dynamical properties in methyl vinyl ether compared to saturated ethers. Normal coordinate calculations of possible rotamers (cis structure force field with certain assumptions has been used) favours the planar trans (or close to it) structure of the second isomer. 相似文献