Liv Fernholt

Structure and barrier of internal rotation of biphenyl derivatives in the gaseous state: Part 1. The molecular structure and normal coordinate analysis of normal biphenyl and pedeuterated biphenyl

Abstract The structures of the title compounds have been determined in the gaseous state. Both static and dynamic models have been applied. The structure parameters are found to be: r(C1C1′) = 1.507(4) and 1.489(4). r(C1C2) = 1.404(4) and 1.403(6), r(C2C3)= 1.395(5) and 1.396(8), r(C3C4) = 1.396(5) and 1.398(13), r(CH) = 1.102(2) and r(CD) = 1.095(2), ∠C2C1C6 = 119.4(4) and 117.9(4), ∠/C1C2C3 = 119.4(4) and 121.3(4) respectively for C12H10 and C12D10. Distances, re, are in A and angles, ∠α, in degrees. Both molecules are non planar with a torsional angle equal to 44.4(1.2) and 45.5(1.6) for C12H10 and C12D10 derived from the dynamic model using the potential function V(o) = (V2/2)(1 − cos 2o) + (V4/2)(1 − cos 4o) where V2 = 0,5(1.1) and -0.6(1.9) kJ mol−13 V4 = −6.2(2.3) and −9.5(3.6) kJ mol−1 for C12H10 and C12D10, respectively. The barriers at O° are 6.0(2.1) and 9.9(3.0) kJ mol−1, and at 90° 6.5(2.0) and 9.2 (2.6) kJ mol−1, respectively for C12H10 and C13D13. Uncertainty is one standard deviation from least-squares refinement using a diagonal weight matrix. With the exception of the torsional angles all the geometrical parameters for C12H10 and C12D10 are the same both comparing the two compounds and the results obtained in the gas phase and in the crystal, the experimental errors taken into consideration.

Structure of cyclohexane determined by two independent gas electron-diffraction investigations

Abstract The results of two independent electron-diffraction investigations of cyclohexane are compared. By averaging the results the following parameters and error limits are obtained: r g (CC) = 1.536±0.002 A, r g (CH) = 1.121±0.004 A, and ∠CCC = 111.4±0.2°.

The molecular structure of di(μ-1-propynyl)bis(dimethylaluminium), [(CH3)2Al(μ-CCCH3)]2, determined by gas phase electron diffraction

Abstract The electron scattering pattern of di(μ-1-propynyl)bis(dimethylaluminium) (I) has been recorded from s = 2.50 to 36.50 A −1 with a nozzle temperature of 88±6 °C. Models of D 2h symmetry (with the CC bonds perpendicular to the Al⋯Al vector) were not compatible with the electron diffraction data. A model of C 2h symmetry could be brought into satisfactory agreement with the data. The structure parameters obtained by least squares calculations on the intensity data suggest that (I) may be regarded as consisting of two somewhat distorted (CH 3 ) 2 AlCCCH 3 units which are joined by donation of π-electrons from the CC bond of each unit into an empty atomic orbital on the Al atom of the other unit.

The molecular structures of gaseous tetramethylurea and tetramethylthiourea as determined by the electron-diffraction method

Abstract Tetramethylurea and tetramethylthiourea have been studied by electron-diffraction in the gas phase. A pyramidal configuration about the N-atoms is found for both molecules with pyramid heights of 27.2 and 11.3 pm for tetramethylurea and tetramethylthiourea, respectively. The most important structural parameters are: (see Fig. 1 for numbering of the atoms and the definition of φ 1 and φ 2 ). Values in parentheses are one standard deviation where correlation among data and uncertainty in the electron wavelength have been included.

The molecular structure of tellurium dichloride, TeCl2, determined by gas electron diffraction

Abstract The electron diffraction pattern of the vapor from a liquid sample ( t = 210°C) of composition Te:Cl = 1.00:2.00 has been recorded. The gas jet was found to consist of TeCl 2 molecules with bond distance TeCl = 2.329(3) A and valence angle ∠ClTeCl = 97.0(6)°.

Structure and barrier to internal rotation of biphenyl derivatives in the gaseous state: Part 2. Structure of 3,3′-dibromo-, 3,5,4′ -tribronio- and 3,5,3′5′ -tetrabromobiphenyl

Abstract Gas-phase electron diffraction structures of the title compounds have been determined. The structure parameters were found to be: 3,3′-Dibromobiphenyl: r(Br) = 1.892(2), r(CC) ave = 1.398(1), r(ClCl′) = 1.504(5), r(CH)ave = 1.093(5), ∠C6C1C2 = 121.4(4), ∠C2C3Br = 119.4(4). 3,5,4′-Tribromobiphenyl: r(C3Br3) = 1.885(2), r(C4Br4′) = 1.892(2), r(C1C2) = 1.396(1), r(C2C3) = 1.399(1), r(C3C4) = 1.396(1), r(C1′C2′) = 1.394(1), r(C2′C3′) = 1.398(1), r(C3′C4′) = 1.394(1), r(C1C1′)_ = 1.511(9), r(C2H2) = 1.065(6), r(C4H4) = 1.070(6), r(C3′H3′) = 1.066(6), ∠C2C1C6 = 120.5(8), ∠C1C2C3 = 118.9(6), ∠C2′C1′C6′ = 120.4(1.0), ∠C1′C2′C3′ = 120.0(2). 3,5,3′5′ -Tetrabromobiphenyl: r(CBr) = 1.889(1), r(C1C2) = 1.395(5), r(C2C3) = 1.389(7), r(C3C4) = 1.406(9), r(C1C1′) = 1.513(9), r(CH) = 1.062(6), ∠C2C1C6= 120.2(5), ∠C1C2C3 = 119.5(2). Distances ra, are given in Angstroms and angle, ∠α, in degrees referring to the dynamic model. Both static and dynamic models have been applied in investigating the large amplitude motion about the inter-ring CC bond. All title compounds are non-planar. The dynamic model (using potential function V(o) = built1 2 V2 (1 −cos 2o) + built1 2 V4(1 − cos 4o)) gave dihedral angles of 43.8(1,3)°, 42.4(2.6)° and 43.7(0.8)°, and Fourier coefficients V2 and V4 equal to 0.8(0.9) and −5.0(1.8), −1.6(1.2) and 4.5(3.7), 1.3(0.8) and −7.0(1.5) kJ mol−1, respectively for 3,3′ -dibromo-,3,5,4,′-tribromo- and 3.5.3′,5′,-tetrabromo-biphenyl. The numbers in parentheses are one standard deviation as given by least-squares refinements using a diagonal weight matrix.

Structure of gaseous tetramethylsuccinic anhydride

Abstract Tetramethylsuccinic anhydride has been studied by gas electron diffraction. A nonplanar ring was obtained, with torsional angles φ(C5O1C2C3) = 10.6 ± 1.5°, φ(01C2C3C4) = 26.5 ± 3.2° and φ(C2C3C4C5) = 30.4 ± 4.0°. Torsional angles calculated by the molecular mechanics method were in fairly good agreement with the experimental values.

The molecular structure of decamethylmanganocene, [η-C5(CH3)5]2Mn, determined by gas phase electron diffraction

The molecular structure of decamethylmanganocene which is in the low spin state 2E2g in the gas phase, has been determined by gas phase electron diffraction. The equilibrium conformation is D5d with staggered ligand rings. The MnC bond distance and root mean square vibrational amplitude are ra = 2.130(4) A and l = 0.076(4) A, respectively.

The Molecular Structure of Selenium Dichloride, SeCl2, Determined by Gas Electron Diffraction

Abstract The electron diffraction pattern of the vapor from a sample of SeCl4 has been recorded with a reservoir and nozzle temperature of about 175 °C. The gas jet was found to consist of SeCl2 (80%) and Cl2 (20%). The bond distance in SeCl2 is ra(Se-Cl) = 2.157(3) Å, the valence angle