Multiconfiguration self-consistent wavefunctions for CH4, C2H4 and C2H6

The results of several MC SCF calculations on CH₄, C₂H₄ and C₂H₆ with minimun bases of Slater type AO's are reported. The computing method is a quadratically convergent process. Better final energies are obtained if localized MO's are used.     

Gas phase electron diffraction study of tetraphenyltin,Sn(C6H5)4

The geometrical parameters of the tetraphenyltin molecule have been determined by gas phase electron diffraction at about 310°. The S₄ and “open” D_2d molecular models with the tetrahedral bond configuration at tin were chosen for the structure analysis. The former gave the better fit. The thermal average bond lengths (r_g, in Å) are as follows:

The benzene ring geometry appears to be almost unaffected by bonding to tin. However, tin causes an increase in the endocyclic valence angle at the ipso-carbon atom to 121.0(0.9)° rather than a decrease of that angle as might be expected, tin being a σ-electron donor. The ring plane and the plane containing the

bond and S₄ axis make an angle, ?, of 34.1(2.1)°. The

bond length in tetraphenyltin is longer than not only the

bond in tetravinyltin (r_g = 2.117(4) Å) but also the

bond in tetramethyltin (r_g = 2.144(7) A).     

Gas phase electron diffraction study of basketene,C10H10

A gas phase electron diffraction study of the cage hydrocarbon, basketene, is reported. A least squares treatment of molecular intensities has been carried out in terms of a geometrically consistent r_α structure. The mean amplitude values and shrinkage corrections have been calculated using the force field parameters estimated from the data on simpler molecules.Structure refinement of the C_2v molecular model yields the following parameter values (bond lengths, r_a, in nm; angles, r_α in degrees): <C₂—C_3, C₄—C₅?_av 0.1609(14); C₃—C₄ 0.1563(6); C₉C₁₀ 0.1360(9); C₁—C₁₀ 0.1511(13); C₁—C₂ 0.1517(9); <C-H>_av. 0.1092(8); <C₃C₄C₇ 88.5(1.0); dihedral angle C₃C₄C₇/C₃C₅C₇ 153.8(1.0). Parenthesized are three times the standard deviation values, 3σ.In addition to the geometric parameters listed, the mean amplitudes for all bonded and C· C nonbonded distances have been determined by the least squares method. All the other amplitudes (C· H and H· H) have been fixed at the values estimated from the spectral data.Comparison of the results obtained with the literature data on similar polycyclic molecules points to the stronger internal strain in the basketene molecule.     

Vapour-liquid equilibrium data for the systems C2H6 + N2, C2H4 + N2, C3H8 + N2, and C3H6 + N2

High pressure vapour-liquid equilibrium data for the C₂H₆ + N₂, C₂H₄ + N₂, C₃H₈ + N₂, and C₃H₆ + N₂ systems are presented. The data are obtained isothermally in the range from 200 K to 290 K. For each point of data, temperature, pressure and liquid and vapour phase mole fractions are measured.Values for the vapour phase mole fractions are calculated from the obtained pressure, temperature and liquid phase mole fractions. The calculated values are compared with the experimental results, and it is found that the average mean deviation between calculated and experimental mole fractions is less than 0.009 for the systems considered in this work.     

Die Trennung von Ar und O2 sowie CH4, C2H6, C3H8 und C4H10

Ohne Zusammenfassung     

The molecular structure of beryllocene, (C5H5)2Be. A reinvestigation by gas phase electron diffraction

The electron scattering pattern of gaseous dicyclopentadienylberyllium, Cp₂Be, has been recorded from s = 2.00 to 39.00 Å⁻¹ with a nozzle temperature of about 120°C. Molecular models of D_5d symmetry or models containing one π-bonded and one σ-bonded Cp ring are not compatible with the data. The possibility the gaseous Cp₂Be consists fo a mixture D_5d and π-Cp, σ-Cp conformers is considered and rejected. A model of C_5v symmetry can be brought into satisfactory agreement with the data. It is also found that a slip sandwich model obtained from the C_5v model by moving sideways the ring which is at the greatest distance from Be, while keeping the two rings essentially parallel is compatible with the electron diffraction data. The best fit between experimental and calculated intensity curves is obtained with a model with a sideways slip of 0.8(1) Å. This model is similar to that indicated by the X-ray diffraction investigations by Wong and coworkers [4,5]. It is suggested that the potential energy of the molecule does not change much as the magnitude of the slip changes and that the molecule thus undergoes large amplitude vibration.     

Reactions of C2(a 3πu) with CH4, C2H2, C2H4, C2H6, and O2 using multiphoton UV excimer laser photolysis

C₂(a ³π_u) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10^?6(x10^?10cm³s^?1) are reported for reactions with C₂H₄, C₂H₂, O₂, C₂H₆, and CH₄, respectively at 298 K. C₂(a ³π_u) fragments are generated by multiphoton ArF excimer laser photodissociation at C₂H₂, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C₂(a ³π_u) → (X ¹σ⁺_g) quenching channel. C₂ + C₂H₂ represents the one possible exception to the reactive channel.     

Kinetic isotope effects in the reaction H + C2H4 → C2H5

The high-pressure limiting rate constants of the reactions between H or D atoms and three isotopic ethylenes have been measured in the temperature range 206–461 K. Practically no isotope effects due to the differences between the ethylenes could be observed. This result does not agree with the prediction recently made by the activated complex theory.     

Singlet-triplet energy separation in divalent seven-membered cyclic conjugated compounds C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb

The electronic and thermal energy differences, ΔE(t-s); enthalpy differences, ΔH(t-s); and free energy differences between the singlet and triplet states, ΔG(t-s), were calculated for C₆H₆C, C₆H₆Si, C₆H₆Ge, C₆H₆Sn, and C₆H₆Pb at the B3LYP/6-311++G (3df, 2p) level. The singlet-triplet splitting, G _s-t, of C₆H₆C, C₆H₆Si, C₆H₆Ge, C₆H₆Sn, and C₆H₆Pb generally increased from C₆H₆C toward C₆H₆Pb. The most stable tautomers and conformers were suggested for the singlet and triplet states of C₆H₆M (M = C, Si, Ge, Sn and Pb). The geometrical parameters were calculated and discussed. The text was submitted by the authors in English.     

Dynamic Jahn–Teller effect and average structure of dicyclopentadienylcobalt, (C5H5)2Co,studied by gas phase electron diffraction

The molecular structure of (C₅H₅)₂Co has been determined by gas phase electron diffraction. The best agreement between calculated and experimental intensity curves is obtained with a model with eclipsed C₅H₅ rings (symmetry D_5h), but a model with staggered rings (symmetry D_5d) cannot be ruled out. The mean CoC and CC bond distances are 2.119(3) Å and 1.429(2) Å respectively. The average angle between the CH bonds and the C₅ ring is 2.1(0.8)°. The value obtained for the CC vibrational amplitude, l(CC) = 0.055(1) Å, is significantly larger than the amplitude calculated from a molecular force field and the corresponding amplitudes in (C₅H₅)₂Fe and (C₅H₅)₂Ni determined by electron diffraction, and confirms the presence of a dynamic Jahn—Teller effect of the magnitude calculated from ESR data. The average structure is compared with those of the metallocenes of the other first row transition elements.     

Surface-enhanced raman spectra of C2H2 and C2H4 adsorbed on silver colloid

We report the surface-enhanced Raman spectra of ethylene and acetylene adsorbed on colloidal silver particles formed by gas aggregation and isolated at low temperatures in solid adsorbate/argon matrices. The spectra of both molecules exhibit modes which are normally Raman-forbidden. Excitation with several visible laser frequencies indicated that the degree of enhancement increased towards the blue.     

Zur Trennung von H2, O2, N2, NO, CO, N2O, CO2, C2H6, C2H4, C2H2, NO2(N2O4) und Feuchtigkeit

Ohne Zusammenfassung     

Evidence for the distortion of C2H4 and C2H2 chemisorbed on W(100)

The adsorption of C₂H₄ on W(100) has been studied by ultraviolet photoelectron spectroscopy with hν = 21.22 eV. The spectrum measured after in initial saturation exposure at 80 K exhibits structure which correlates well with energy levels recently calculated by Demuth and Eastman (DE) for sp³ rehybridized C₂H₄. Dehydrogenation of the adsorbate, either by subsequent heating to 295 K or direct adsorption at 295 K, yields a spectrum which correlates with DE's calculation for sp² rehybridized C₂H₂. These results suggest that C₂H₄ and C₂H₂ may be distorted from their planar and linear structures respectively and that the CC bonds on these molecules are stretched by adsorption on W(100). Qualitative arguments suggest that the bonding site for both melecules is directly over a W atom and that the Dewar—Chatt model for πd bonding in organometallic compounds is applicable.     

Experimental and Theoretical Study of Hydrogen Atom Abstraction from C2H6 and C4H10 by Zirconium Oxide Clusters Anions

The reactions of anionic zirconium oxide clusters Zr_xO_y^- with C₂H₆ and C₄H₁₀ are investi-gated by a time of flight mass spectrometer coupled with a laser vaporization cluster source.Hydrogen containing products Zr₂O₅H^- and Zr₃O₇H^- are observed after the reaction. Den-sity functional theory calculations indicate that the hydrogen abstraction is favorable in the reaction of Zr₂O₅^- with C₂H₆, which supports that the observed Zr₂O₅H^- and Zr₃O₇H^- are due to hydrogen atom abstraction from the alkane molecules. This work shows a newpossible pathway in the reaction of zirconium oxide cluster anions with alkane molecules.     

Synthesis, structural characterization and reactivity of the amino borane 1-(NPh2)-2-[B(C6F5)2]C6H4

The bright red title compound 1 was synthesized from (2-lithiophenyl)diphenylamine and bis(pentafluorophenyl)boron chloride. Its reactions with small acids like H₂O and HCl proceeded easily giving zwitterionic compounds. For 1 and its water adduct 2 the crystal structures were determined, the latter featuring an ammonium borate structure containing a short intramolecular hydrogen bond bridge. Treatment of 1 with Jutzi's acid, [H(OEt₂)₂][B(C₆F₅)₄], did not result in protonation of the nitrogen, but reaction of 1 with LiH in the presence of 12-crown-4, led to the isolation of the aminoborate [1-(Ph₂N)-2-{B(H)(C₆F₅)₂}C₆H₄][Li(12-crown-4)] (3). Borohydride 3 reacted with Jutzi's acid to regenerate 1 and liberate hydrogen.     

Chiral “P-N-P” ligands, (C20H12O2)PN(R)PY2 [R = CHMe2, Y = C6H5, OC6H5, OC6H4-4-Me, OC6H4-4-OMe or OC6H4-4-Bu] and their allyl palladium complexes

Chiral “P-N-P” ligands, (C₂₀H₁₂O₂)PN(R)PY₂ [R = CHMe₂, Y = C₆H₅ (1), OC₆H₅ (2), OC₆H₄-4-Me (3), OC₆H₄-4-OMe (4) or OC₆H₄-4-^tBu (5)] bearing the axially chiral 1,1′-binaphthyl-2,2′-dioxy moiety have been synthesised. Palladium allyl chemistry of two of these chiral ligands (1 and 2) has been investigated. The structures of isomeric η³-allyl palladium complexes, (R′ = Me or Ph; Y = C₆H₅ or OC₆H₅) have been elucidated by high field two-dimensional NMR spectroscopy. The solid state structure of [Pd(η³-1,3-Ph₂-C₃H₃){κ²-(racemic)-(C₂₀H₁₂O₂)PN(CHMe₂)PPh₂}](PF₆) has been determined by X-ray crystallography. Preliminary investigations show that the diphosphazanes, 1 and 2 function as efficient auxiliary ligands for catalytic allylic alkylation but give rise to only moderate levels of enantiomeric excess.     

Synthesis and crystal structures of (C8h8)Nd(C5H9C5H4) (THF)2 and [(C8H8)Gd(C5H9C4H4(THF)][(C8H8)GD(C5H9C5H4(THF)2]

LnCl₃ (Ln=Nd, Gd) reacts with C₅H₉C₅H₄Na (or K₂C₈H₈) in THF (C₅H₉C₅H₄ = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C₅H₉C₅H₄)LnCl₂(THF)_n (orC₈H₈)LnCl₂(THF)_n], which further reacts with K₂C₈H₈ (or C₅H₉C₅H₄Na) in THF to form the litle complexes. If Ln=Nd the complex (C₈H₈)Nd(C₅H₉C₅H₄)(THF)₂ (a) was obtained: when Ln=Gd the 1 : 1 complex [(C₈H₈)Gd(C_%H₉)(THF)][(C₈H₈)Gd(C₅H₉H₄)(THF)₂] (b) was obtained in crystalline form.

The crystal structure analysis shows that in (C₈H₈)Ln(C₅H₉C₅H₄)(THF)₂ (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η⁵), cyclooctatetraenyl (η⁸) and two oxygen atoms from THF are coordinated to Nd³⁺ (or Gd³⁺) with coordination number 10.

The centroid of the cyclopentadienyl ring (Cp′) in C₅H₉C₅H₄ group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd³⁺ (or Gd³⁺). In (C₈H₈)Gd(C₅H₉C₅H₄)(THF), the cyclopentyl-cyclopentadienyl (η⁵), cyclooctatetraenyl (η⁸) and one oxygen atom are coordinated to Gd³⁺ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd³⁺, which is almost in the plane (dev. -0.0144 Å).     

Cationic rhodium tetrafluorobenzobarrelene complexes with diolefin or arene ligands,crystal structures of [Rh(TFB)(arene)] ClO4, (arene = C6Me6, C6H3Me3, C6H4Me2)

The preparation and properties of complexes of the general formulae [Rh(TFB)(diolefin)]ClO₄, [Rh(TFB)(arene)]ClO₄ and [Rh(TFB)L₂]ClO₄, (TFB = tetrafluorobenzobarrelene, L = dimethylsulfoxide and tetrahydrothiophen) are described. The crystal structures of the arene complexes (arene = C₆Me₆, C₆H₃Me₃ and C₆H₄Me₂) have been solved by X-ray methods. The three compounds crystallize in quite similar lattices: R3c, a = b = 27.122, 26.233, 25.731 and c = 17.079, 16.388, 16.256 Å, respectively. δR-plots for about 2000 reflections show the agreement in the refinements carried out up to R-values of 5%, 5% and 4% respectively. The Rh atom is coordinated to the double bonds of the TFB and to the arene ring in all three compounds, but the deviation from planarity of the arene and its relative position with respect to the TFB moiety varies.     

Measurement of the Compton profiles of CH4 and C2H4 by high energy electron impact spectroscopy

We present a new experimental determination of the Compton profiles of CH₄ and C₂H₄ molecules using high energy electron impact. The observable q range has been extended up to 10 au (6 au for C₂H₄). Good agreement is found with an earlier X-ray scattering experiment and with new theoretical calculations.     

The ground-state singlet potential surface for C2H4

Calculations with an extended polarized basis set and Møller-Plesset perturbation theory including triple substitution correlation corrections in the fourth-order treatment indicate that singlet ethylidene (CH₃CH:) is not a local minimum on the C₂H₄ potential energy surface. Rearrangement to ethylene occurs without actuation. Barriers for hydrogen scrambling and for 1,1-hydrogen elimination are estimated.