Electronic States of 1,5-Cyclooctadiyne Radical Cation and of Related Systems: The electronic structure of cis-bent carbon-carbon triple bonds

The photoelectron spectra of 1,5-cyclooctadiyne ( 2 ) and of 1,6-dithiacyclodeca-3,8-diyne ( 3 ) have been recorded. The first four ( 2 ) or six ( 3 ) PE. bands have been assigned as follows; in increasing order of ionization potentials: The relative sequence and the positions of the PE. bands are explained in terms of through-bond and through-space interactions between the basis π-orbitals and σ-orbitals of appropriate symmetry behaviour. An analysis of the PE. spectroscopic data for cyclooctyne ( 1 ) and for ( 2 ) indicates that a cis-bend of the acetylene moiety by θ < 20° leads to a split in energy of the in-plane and out-of-plane basis π-orbitals which is smaller than ∽ 0.2 eV. This is in agreement with the predictions derived from semiempirical models (MINDO/2, SPINDO) and qualitative orbital arguments. However, it is shown by using orbital localization procedures, that the rationales underlying the two semiempirical models differ significantly.     

A Quantitative Assessment of „Through-space”︁ and „Through-bond”︁ Interactions. Application to Semi-empirical SCF Models

The scheme of ‘through-space’ and ‘through-bond’ interaction of (semi)localized orbitals, originally proposed by Hoffmann, is reexamined in terms of SCF many-electron treatments. It is shown that the two types of interaction can be characterized by examining the corresponding off-diagonal matrix elements of the Hartree-Fock matrices of the localized or the symmetry adapted localized orbitals and of the partially diagonalized Hartree-Fock matrices referring to ‘precanonical orbitals’. The procedure outlined is applied to three practical examples using the semiempirical many-electron treatments SPINDO, MINDO/2 and CNDO/2:

• a A reassessment of ‘through-space’ and ‘through-bond’ interaction in norbornadiene indicates, that the latter type of interaction is also of importance for the orbital based mainly on the antisymmetric combination of the localized x-orbitals. The differences in the predictions derived from the three models are critically examined.
• b The competition between ‘through-space’ and ‘through-bond’ interaction in the series of bicyclic dienes from norbornadiene to bicyclo[4.2.2]-dcca-7,9-diene and in cyclohexa-1,4-diene, i. e. their dependence on the dihedral angle UI is reexamined. It is found that the rationalization for the orbital crossing near ω = 130° deduccd from PE. spectroscopic data can not be as simple as originally suggested and that the relay’ orbitals responsible for ‘through-bond interaction affecting both the symmetric and the antisymmetric combination of the π-orbitals extend over the whole CC-σ-system of the six membered ring.
• c ‘Through-bond’ interaction of the two lone pair orbitals in 1,4-diazabicyclo[2.2.2]octane is found to be large for their symmetric and the antisymmetric linear combination.

The analysis quoted, draws attention to some of the dangers involved in using semiempirical treatments for the interpretation of PE. data in terms of Koopmans′ theorem, without due caution.     

Generalized Gibbs’ approach to the thermodynamics of heterogeneous systems and the kinetics of first-order phase transitions

In the theoretical interpretation of the kinetics of first-order phase transitions, thermodynamic concepts are widely employed that were developed long ago by Gibbs and van der Waals. However, the results of such analysis are partly unsatisfactory and internally contradictory. By generalizing Gibbs’ approach, the existing deficiencies and internal contradictions of these two well-established theories can be removed and a new generally applicable tool for the interpretation of these processes can be developed. The basic ideas of the generalized Gibbs approach and a variety of consequences obtained on its basis with respect to the understanding of the general features of the kinetics of first-order phase transitions are outlined. Dedicated to the memory of Vladimir P. Skripov. The text was submitted by the authors in English.     

Elastic stress effects on critical cluster shapes

Crystallization of solids at planar solid–air surfaces was analyzed. Shape and size of clusters of the newly evolving phase are determined which correspond to the minimal work of cluster formation in nucleation. Both elastic field and surface energy terms are taken into consideration. This work is not restricted to the consideration of spherical interfaces cluster–ambient solid phase but allows, more general arbitrary shapes of the new phase. Application to crystallization of glassforming melts, gives additional support to the idea that differences in the degree of evolution of elastic strains in crystallization in the bulk and near external or internal surfaces of highly viscous glassforming melts in the vicinity of the temperature of vitrification T_g may be the origin for the preferential surface crystallization of glasses.     

Prediction of vapour-liquid equilibria for systems containing longer-chain alcohols and alkanes by various group-contribution methods

Comparisons are made of predicted excess free enthalpies provided by the parameters available for the ASOG model of Derr and Deal, the UNIFAC model of Fredenslund et al., and the CRG (chemical-reticular group-contribution) method of Neau and Péneloux. These methods are applied to predict vapour-liquid equilibria for alcohol-alkane systems having carbon numbers up to 16. Overall, the accuracy of prediction increases in the order UNIFAC, ASOG, CRG.     

Overlaps in Pilot Wave Field Theories

Recently doubts have been raised about the ability of pilot wave theories with field ontology to recover the predictions of quantum field theory. In particular, Struyve has questioned that the overlap between wave functionals of macroscopically different states with fixed particle number is really non-significant.