Sven J. Cyvin

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.

Advances in the Theory of Benzenoid Hydrocarbons

Topological properties of benzenoid systems.- Total ?-electron energy of benzenoid hydrocarbons.- Enumeration of benzenoid systems and other polyhexes.- Benzenoid chemical isomers and their enumeration.

Molecular vibrations of footballene

Abstract A normal coordinate analysis has been carried out for C 60 “footballene”. A five-parameter force field was employed in order to calculate the vibrational frequencies. Results for the 10 Raman-active and 4 infrared-active frequencies are reported.

Symmetry Coordinates, Harmonic Force Field, and Mean Amplitudes for Light and Heavy Dibenzene Chromium

The molecular vibrations of dibenzene chromium are analyzed in terms of the eclipsed 25 atomic model of symmetry D6h with planar ligands. A complete set of symmetry coordinates is constructed and based almost entirely on conventional types of valence coordinates. A harmonic force field is given, and is used to calculate the vibrational frequencies, mean amplitudes of vibration, and perpendicular amplitude correction coefficients for (C6H6)2Cr and (C6D6)2Cr.

“Crowns”, and aromatic sextets in primitive coronoid hydrocarbons

SummaryA type of graphs derived from a cycle and associated with primitive coronoids are referred to as “crowns”. The characteristic polynomials and matching polynomials of crowns are studied. These notions are used to calculate the sextet polynomial for primitive coronoids. Patterns of aromatic sextets are treated in some detail.ZusammenfassungEine Graphentype, die von einem Cyclus abgeleitet ist und mit einfachen Coronoiden verknüpft ist, wird als “Crown” bezeichnet. Die charakteristischen Polynome und die „matching“ Polynome der Crowns werden untersucht. In diesem Rahmen werden die Sextett-Polynome für einfache Coronoide berechnet. Die Muster der aromatischen Sextette werden im Detail behandelt.

Structure and conformations of isoprene by vibrational spectroscopy and gas electron diffraction

Abstract The structure of the isoprene (2-methyl-buta-1,3-diene) molecule has been studied by vibrational spectroscopy and gas electron diffraction techniques. A normal coordinate analysis was used to calculate the vibrational frequencies for the anti ( s-trans ), gauche and syn ( s-cis ) conformers of the molecule. Assignments of some frequencies of the anti form were revised. The experimental bands at 1255, 635, 555, 419 and 311 cm −1 are assigned as fundamentals of the gauche conformer with a high degree of confidence. Among the structural parameters determined by electron diffraction are the following bond distances (in A): CC 1.340, CC 1.463, CC methyl 1.512, CH 1.076 and C methyl H 1.110. The abundance of the anti form was determined to be 95.3%, while the rest (4.7%) was interpreted as the gauche form with a dihedral angle of 73.5°.

The vibrational spectra of maleic anhydride and its deuterated species

Abstract The infrared spectra of maleic anhydride and its mono- and dideuterated species were recorded in the region 5000-50 cm −1 in the vapour phase and in solution. Raman spectra of the solids and supercooled melts were obtained. Assignments of the fundamental vibrational frequencies are given, based upon semiquantitative polarization data and the infrared vapour contours as well as on the product rule and complete isotopic rule for the three compounds.

Normal coordinate analysis of the total ferrocene complex

The results of a total normal coordinate analysis of ferrocene, Fe(C5H5)2, are reported. As in a previously published total vibrational analysis of dibenzenechromium, interesting kinematic couplings between some ligand and some framework normal modes of the complex can be observed, and these account for some frequency shifts from free (ionic) to complexed cyclopentadienide without any charge in the harmonic force field of the ligand. Calculated mean amplitudes for ferrocene are compared with those determined by an electron diffraction study and with the corresponding values in the free cyclopentadienide anion.

Number of kekulé structures of single-chain corona-condensed benzenoids (cycloarenes)

Abstract Explicit formulas are given for the number of Kekule structures of some classes of corona-condensed benzenoids. A general algorithm for cycloarenes is reported.

Enumeration and classification of coronoid hydrocarbons: Part V. Primitive coronoids

Some topological properties of primitive coronoids are discussed. A method of generating such systems from the corona hole is described in detail. The results from computer-aided enumerations of primitive coronoids are given for h (the number of hexagons ) up to 25. The results account for 1 075 554 nonisomorphic systems. The distributions into symmetry groups are specified. The forms of all the primitive coronoids for h ⩽ 15 are depicted and supplied with K numbers ( Kekule structure counts ). Finally the average K values and related quantities for the systems under consideration are reported.