The molecular orbital theory of chemical valency. III. Properties of molecular orbitals

1950 ◽  
Vol 202 (1069) ◽  
pp. 155-165 ◽  
Keyword(s):  
Perturbation Theory ◽  
Molecular Orbital ◽  
Molecular Orbitals ◽  
Molecular Properties ◽  
The Other ◽  
Molecular Orbital Theory ◽  
Special Significance ◽  
Orbital Theory ◽  
Molecular Systems ◽  
Normal States

The discussion of molecular orbitals and equivalent orbitals, given in previous papers, is carried a stage further. It is shown that certain molecular properties can be evaluated using either equivalent or molecular orbitals. On the other hand, a study of the changes produced by ionization demonstrates that molecular orbitals have a special significance and that certain energy parameters associated with them are closely related to ionization potentials. For the purpose of this discussion a perturbation theory is developed to deal with the changes produced in molecular systems when disturbed from their normal states.

Molecular Orbitals and CH3, CH2, and CH Deformation Group Frequencies

1980 ◽  
Vol 34 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Norman B. Colthup
Keyword(s):  
Linear Relationship ◽  
Electron Density ◽  
Force Constant ◽  
Molecular Orbital ◽  
Interaction Force ◽  
Molecular Orbitals ◽  
Deformation Vibration ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Symmetrical Deformation

A linear relationship has been found between the wavenumber of the CH3 symmetrical deformation vibration and the electron density on the CH3 carbon as calculated from CNDO/2 molecular orbital theory. Other CH deformation vibrations are also related to the electron density on the carbon and, as a result, can be correlated with the CH3 symmetrical deformation wavenumber. These include ν̄(CH2 def), ν̄(CH2 wag) and both components of ν̄(CH wag). The splitting of ν̄(CH3 sym def) in isopropyl and t-butyl groups has long been known. It is shown here that the effect is due to an interaction force constant relating to the CH3 symmetrical deformation vibrations of two or three different neighboring CH3 groups. The origin of the interaction is thought to be an H,H′ repulsion between hydrogens on the different CH3 groups.

scholarly journals The determination of molecular orbitals

1949 ◽  
Vol 198 (1052) ◽  
pp. 1-13 ◽  
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbitals ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Energy States ◽  
Molecular Framework

In the molecular orbital theory of valency the electrons are assigned to the whole molecule rather than to atoms or to other localized parts. While the method has advantages in dealing with the properties of a molecule as a whole, such as its energy states, the extension of each orbital over the molecular framework is a disadvantage when dealing with localized properties such as directed bonds. This paper deals in a general way with the equations which molecular orbitals must satisfy, allowing for the exchange of electrons between orbitals. It is then shown that when molecules have properties of symmetry the equations can be transformed so as to be satisfied by orbitals which have the property of equivalence. These can be regarded under certain conditions as directed orbitals and the conditions for these are discussed. To illustrate the method molecules of the type XY 2 are considered.

The molecular orbital theory of chemical valency XIV. Paired electrons in the presence of two unlike attracting centres

1953 ◽  
Vol 218 (1134) ◽  
pp. 327-333 ◽  
Keyword(s):  
Perturbation Method ◽  
Molecular Orbital ◽  
Essential Feature ◽  
Formal Solution ◽  
Wave Functions ◽  
The Other ◽  
Molecular Orbital Theory ◽  
Chemical Bonds ◽  
Orbital Theory ◽  
Antisymmetric Part

As a step towards an understanding of chemical bonds in diatomic molecules which contain unlike atoms, a theory of paired electrons in the presence of two unlike attractive centres has been worked out. The essential feature of the method is that the field of these centres is expressed as a sum of two fields, one of which is symmetrical and the other antisymmetrical in the plane midway between the two centres. A formal solution having been provided in earlier papers for the wave functions and energies of two electrons in the symmetrical part of the field, this is used as a basis for a perturbation method to calculate the effect of the antisymmetric part of the field.

The molecular orbital theory of chemical valency. IV. The significance of equivalent orbitals

1950 ◽  
Vol 202 (1069) ◽  
pp. 166-180 ◽  
Keyword(s):  
Total Energy ◽  
Molecular Orbital ◽  
Molecular Orbitals ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
General Transformation ◽  
Lone Pairs ◽  
Simple Molecules

The theory of the transformation from molecular orbitals to sets of equivalent orbitals is discussed for the general case when there is more than one occupied molecular orbital of given symmetry and more than one equivalent set. The general transformation is worked out for molecules whose component atoms possess inner shells and lone pairs of electrons. The theory is illustrated by reference to some simple molecules such as water and ammonia. Finally, it is shown how the expression for the total energy of a molecule can be divided up in such a way that the interactions between its localized parts are dealt with separately. The significance of lone pairs of electrons in determining the shape of molecules is pointed out.

scholarly journals How amino and nitro substituents direct electrophilic aromatic substitution in benzene: an explanation with Kohn–Sham molecular orbital theory and Voronoi deformation density analysis

2016 ◽  
Vol 18 (17) ◽  
pp. 11624-11633 ◽  
Author(s):  
O. A. Stasyuk ◽  
H. Szatylowicz ◽  
T. M. Krygowski ◽  
C. Fonseca Guerra
Keyword(s):  
Molecular Orbital ◽  
Electrophilic Substitution ◽  
Molecular Orbitals ◽  
Electrophilic Aromatic Substitution ◽  
Molecular Orbital Theory ◽  
Aromatic Substitution ◽  
Orbital Theory ◽  
Deformation Density ◽  
Density Analysis

Molecular orbitals of aniline explain electrophilic substitution, whereas for nitrobenzene charge rearrangements are needed.

Perspectives on the Role of the Frontier Effective-for-Reaction Molecular Orbital (FERMO) in the Study of Chemical Reactivity: An Updated Review

2020 ◽  
Vol 24 (3) ◽  
pp. 314-331 ◽  
Author(s):  
Letícia S. Braga ◽  
Daniel H. S. Leal ◽  
Kamil Kuca ◽  
Teodorico C. Ramalho
Keyword(s):  
Molecular Orbital ◽  
Chemical Reactions ◽  
Chemical Reactivity ◽  
Molecular Orbitals ◽  
Frontier Molecular Orbital ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Highest Occupied Molecular Orbital ◽  
Lowest Unoccupied Molecular Orbital

Molecular orbitals are critical in the rationalization of several chemical reactions. Thus, the frontier molecular orbital theory, proposed by Fukui's group, postulated the importance of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) for chemical reactions. It should be kept in mind, however, that there are limitations of this theory and new perspectives about the chemical reactivity have recently been arisen based on composition and location of other frontier molecular orbitals. In this review, we have reported the development and the most recent applications of the Frontier Effective-for-Reaction Molecular Orbital (FERMO) concept, which describes the breaking and formation of new chemical bonds and can in turn, provide important clues that modulate chemical reactivity of atoms and molecules.

scholarly journals Linnett Double Quartet Theory, Challenging the Pairing Electrons

2009 ◽  
Vol 6 (1) ◽  
pp. 169-176
Author(s):  
Yeganeh Khaniani ◽  
Alireza Badiei
Keyword(s):  
Molecular Structure ◽  
Electronic Structure ◽  
Molecular Orbital ◽  
Transition States ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Molecular Systems ◽  
Basic Ideas

Linnett proposed his theory 45 years after Lewis's supposition. During these years Pauling, Mulliken and Hund made different molecular structure models based on valance bond and molecular orbital theory. Their theories were seemed to fit many experiences but had some inabilities. Linnett's double quartet theory could solved some important problems about stability of radicals, paramagnetism / diamagnetism in molecular systems, electronic structure in transition states and finally challenge of resonance and aromaticity. In this article we review some basic ideas and concepts concerning different models and then we give a detailed discussion of the LDQ and use it in diverse branches of chemistry.

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