ChemInform Abstract: THE VALENCE-BOND DESCRIPTION OF CONJUGATED MOLECULES. 40. THEORETICAL STUDY OF THE MILLS-NIXON EFFECT, A PHENOMENON OF Π-BOND LOCALIZATION IN SMALL RING ANNELATED AROMATICS

1985 ◽  
Vol 16 (38) ◽  
Author(s):  
P. C. HIBERTY ◽  
G. OHANESSIAN ◽  
F. DELBECQ
Keyword(s):  
Theoretical Study ◽  
Valence Bond ◽  
Small Ring ◽  
Conjugated Molecules ◽  
Bond Localization

Polar structures in the theory of conjugated molecules I. Identification of the ethylene π-electron states

1950 ◽  
Vol 200 (1061) ◽  
pp. 272-283 ◽  
Keyword(s):  
Theoretical Study ◽  
Energy Levels ◽  
Wave Length ◽  
Valence Bond ◽  
Weak Band ◽  
Conjugated Molecules ◽  
Valence Bond Theory ◽  
Aromatic Molecules ◽  
Long Wave ◽  
Bond Theory

This and two of three parts to be published subsequently are concerned mainly with the so-called valence-bond theory of conjugated and aromatic molecules. An improvement to the method is described, which consists in adding to the usual set of structures some extra ones which are ‘polar’ in the sense that they show two of the π-electrons on one centre, and none on another centre, making these two centres carry respectively negative and positive charges. This adds a certain flexibility to the description of molecular states which is lacking when the electrons are supposed to be distributed one to each centre throughout. In this part a preliminary question is treated which bears on getting the new empirical parameters needed for including polar structures in the theory. This question is the assignment of the long wave-length bands in the spectrum of ethylene. The assignment is made with the help of a theoretical study of the ethylene energy levels in an approximation using antisymmetric molecular orbitals. Using this calculation as a guide, two transitions are assigned. A weak band, appearing at about 2000 Å, is taken to be 1 A g - 1 A g9 and a strong one, having its maximum at about 1630 Å, is taken to be 1 A g – 1 B lu .

Polar structures in the theory of conjugated molecules. II. Symmetry properties and matrix elements for polar structures

1950 ◽  
Vol 200 (1062) ◽  
pp. 390-401 ◽  
Keyword(s):  
Valence Bond ◽  
Matrix Elements ◽  
Conjugated Molecules ◽  
Energy Calculations ◽  
Valence Bond Theory ◽  
Energy Parameters ◽  
Symmetry Properties ◽  
The Matrix ◽  
Bond Theory ◽  
Usual Formalism

The inclusion of polar structures in the valence-bond theory of π-electrons entails some additions to the usual formalism, and these are given in this part. The symmetry properties of sets of structures, both non-polar and polar, and the matrix elements that come into energy calculations, are dealt with. Using the work of part I, and the conclusions of this part, the energy parameters for work with polar structures are evaluated.

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