B. N. 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.

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.

“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.

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.

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.

Molecular vibrations of complexes with trigonal ligands: VI: Tetrammines with a square-planar-skeleton- the infrared spectrum of [Cu(15NH3)4]2+

Abstract A vibrational analysis is performed for [Cu(NH3)4]2+, which has a square-planar frame work structure. Two versions of symmetry coordinates are produced assuming the C4V and C4h structures, respectively. The IR spectrum of [Cu(15NH3)4]2+ was recorded, and the observed frequencies used as supplementary data in a normal coordinate analysis along with data available for other isotopic compounds. An approximate force field which reproduces satisfactorily the observed frequencies for all the isotopic compounds is developed. The force constants may be classified as pertaining to the (a) ligand vibrations, (b) ligand-framework couplings and (c) framework vibrations. These calculations for the whole complex are compared with (i) results for free NH3, (ii) the analysis of the XY4 (D4h) point-mass model and (iii) calculations for the pyramidal-axial CuNH3 (C3V) fragment. It is concluded that the effects of kinematic coupling are small. The validity of the point-mass model approximation is confirmed.

Molecular vibrations of free and complexed ligands: the tetramminezinc(II) ion

Abstract The free NH 3 molecule and the [Zn(NH 3 ) 4 ] 2+ ion were studied by the kinematic coupling approach. The pure effects of this coupling were found to be small, and some modifications had to be introduced in order to get a reasonable force field. The force constants deduced for the skeletal vibrations are comparable with those of a quasi-exact force field. Calculated frequencies for [ 68 Zn(NH 3 ) 4 ] 2+ and [ 64 Zn(ND 3 ) 4 ] 2+ are reported in addition to those of [ 64 Zn(NH 3 ) 4 ] 2+ . Mean amplitudes of vibration for [ 64 Zn(NH 3 ) 4 ] 2+ are given.

Enumeration of branched catacondensed benzenoid hydrocarbons and their numbers of Kekulé structures

Abstract The computerized enumerations of unbranched catafusenes (catacondensed benzenoids) are summarized. The systems are classified according to symmetry. The numbers of helicenie systems are given explicitly. The results of enumerations for branched catafusenes are also reported, and the systems without helicenes for 4 h denotes the number of hexagons. For the branched catafuaenes without belicenes all Kekule structure counts (K) were computed. Some characteristic values of K K min , K > K abund , K max are discussed. The subscripts refer to the minimum, most abundant and maximum value. K > is the average. As one of the original results it was found K max 504 for h=12. This K number is realized in two isoarithmic branched catafusenes. Quantities of the type (1n K )/h display especially interesting behaviour.

The molecular structure, conformation and vibrational amplitudes of 1,5-hexadiyne (bipropargyl) in the vapour phase

Abstract The molecular structure and conformation of 1,5-hexadiyne have been studied by the gas electron diffraction method. The molecules were found to exist in an anti/gauche conformational mixture, with the anti conformer very predominant (75 ± 10% anti conformer). The observed conformational composition was correlated with the magnitude of the gauche dihedral angle and the mean vibrational amplitudes of the C1C5 and C1C6 distances of the anti conformer.