The π-Electron distribution in Pyridine and the molecular-orbital parameters for nitrogen

1957 ◽  
Vol 10 (3) ◽  
pp. 211 ◽  
Author(s):  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Molecular Orbital ◽  
Electron Distribution ◽  
Chemical Properties ◽  
Electron Interaction ◽  
Orbital Method ◽  
Orbital Theory ◽  
Orbital Parameters ◽  
Self Consistent Field ◽  
Electron Effects ◽  
Coulomb Parameter

The π-electron distribution in pyridine has been calculated by the self-consistent-field molecular-orbital method, including electron interaction explicitly. Empirical parameters analogous to the coulomb parameters in the simple molecular-orbital theory are not required in the calculations. The results have been compared with chemical properties of pyridine and have also been used to determine the most suitable values for the coulomb parameters in the simple molecular-orbital treatment of pyridine. It emerges that, in addition to a coulomb parameter to allow for the eleotronegativity of nitrogen being greater than that of carbon, an appreciable auxiliary coulomb parameter, representing an enhanced electronegativity of carbon atoms adjacent to the hetero-atom, must be introduced. This auxiliary parameter is necessary to allow for purely π-electron effects in the vicinity of a hetero-atom and is additional to any parameter which might be required owing to σ-electron polarization effects around the nitrogen atom.

A theoretical study of the chemisty of Furan, Phrrole, Benzofuran, Indole, Dibenzofuran, and Carbazole

1959 ◽  
Vol 12 (2) ◽  
pp. 152 ◽  
Author(s):  
RD Brown ◽  
AW Coller
Keyword(s):  
Molecular Orbital ◽  
Orbital Method ◽  
Field Calculation ◽  
The Core ◽  
Oxygen Heterocycles ◽  
Inductive Effects ◽  
Electron Distributions ◽  
Self Consistent Field ◽  
Special Case ◽  
Coulomb Parameter

It is shown that it is possible, within the framework of the simple H�ckel molecular- orbital method, to account fully for all observations on electrophilic substitution in furan, pyrrole, benzofuran, indole, dibenzofuran, and carbazole, in terms of the π-electron distributions in these compounds. The values of coulomb parameters required to obtain this correlation are physically reasonable and in particular are in agreement with values found independently by a variable electronegativity self-consistent field calculation on pyrrole. The previously puzzling difference in orientation of substitution in benzofuran and indole is accounted for in the present study in terms of a difference in the auxiliary inductive effects of the two hetero-atoms. It seems possible to attribute this difference ultimately to differences in the CO and CN bond lengths and to differences in the effective nuclear charges for 2pπ atomic orbitals on the two hetero-atoms. Attention is drawn to an " isoprotonic principle " for estimating the value of the primary coulomb parameter of a hetero-atom. (It is probably a special case of a more general principle-that the primary coulomb parameter is predominantly determined by the charge on the core and scarcely depends upon the nature of the nucleus at the centre of the core.) A spurious H�ckel molecular-orbital model for the oxygen heterocycles is noted. It accounts for the chemistry of the heterocycles but represents a physically unsatisfactory view of the electronic properties of oxygen in these compounds.

scholarly journals LOCALLY PROJECTED MOLECULAR ORBITAL THEORY FOR MOLECULAR INTERACTION WITH A HIGH-SPIN OPEN-SHELL MOLECULE

2006 ◽  
Vol 05 (04) ◽  
pp. 819-833 ◽  
Author(s):  
SUEHIRO IWATA
Keyword(s):  
Molecular Orbital ◽  
High Spin ◽  
Closed Shell ◽  
Open Shell ◽  
Coefficient Matrix ◽  
Molecular Orbitals ◽  
Orbital Method ◽  
Stationary Condition ◽  
Orbital Theory ◽  
Stationary Conditions

Locally projected molecular orbital method for molecular interactions is extended to a cluster consisting of a high-spin open-shell molecule and many closed-shell molecules. While deriving the equations, the Hartee–Fock–Roothaan equation without the orthonormal condition is obtained. The stationary conditions for molecular orbitals are expressed in a form of a generalized Brillouin condition. To obtain the molecular orbital coefficient matrix, which satisfies the stationary condition, a single Fock operator form is presented. For the locally projected molecular orbitals for the open-shell cluster, the working matrix representaion is given.

The nature of the sulphur-oxygen bond

1950 ◽  
Vol 200 (1062) ◽  
pp. 409-428 ◽  
Keyword(s):  
Molecular Orbital ◽  
Electronic Structures ◽  
Chemical Properties ◽  
Orbital Method ◽  
Physical And Chemical Properties ◽  
Bond Strengths ◽  
Set Up ◽  
Physical And Chemical ◽  
Oxygen Bond ◽  
And Chemical Properties

The electronic structures of certain molecules containing oxy-sulphur bonds are analyzed insome detail by means of the molecular orbital method. I t is possible to make rough calculations which, despite the complexity of the system s considered, are nevertheless reasonably reliable. The physical and chemical properties of sulphur dioxide, sulphur trioxide and molecules of the types R 2 SO 2 and R 2 SO are discussed on the basis of these structures. In all these molecules it appears that the oxy-sulphur linkages are best described as double-bonded. A successful correlation between the molecular orbital criterion of bond strengths, namely, the bond orders, and the oxy-sulphur bond force constants may be set up. The measure of agreement attained between observed and predicted properties is quite satisfactory.

The Electronic Structures of A2Y4 Molecules

1963 ◽  
Vol 16 (5) ◽  
pp. 737 ◽  
Author(s):  
RD Brown ◽  
RD Harcourt
Keyword(s):  
Molecular Orbital ◽  
Electronic Structures ◽  
Lone Pair ◽  
Orbital Method ◽  
Molecular Orbital Theory ◽  
Bond Properties ◽  
Orbital Theory ◽  
The Core ◽  
Valence Electrons ◽  
Charge Rule

A study of the electronic structures of A2Y4 molecules containing 34, 36, and 38 valence electrons has been made. An approximate VESCF, molecular- orbital method was used, attention being concentrated mainly on the delocalization of σ-electrons which are classically regarded as lone-pairs on the Y atoms. The results provide explanations of the main features of many of the observed AA- and AY-bond lengths and YAY-bond angles of N2O4, C2O42-, B2F4, B2Cl4, C2F4, C2Cl4, S2O42-, and N2F4. Other A2Y4 systems which have either not been fully characterized or not yet reported are also considered. The extent of lone-pair delocalization is shown to be governed by a parameter aσ, related to the coulomb and resonance parameters of H�ckel molecular-orbital theory. General trends in the value of aσ can be predicted from values of the core charges of A and Y towards the o-electrons concerned. A more detailed "adjacent charge" rule emerges. It differs from the classical rule in that for A2Y4 systems, adjacent negative formal charges on the A atoms should not very greatly affect the AA-bond properties. Difficulties were encountered in consistently interpreting the properties of some A2F4 and A2Cl4 compounds. These deserve further attention.

A test of the bay-region mechanism in carcinogenesis for monomethyl benz[a]anthracenes in a self-consistent-field molecular orbital theory

1986 ◽  
Vol 175 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Rabi Majumdar ◽  
Ashoke R. Thakur ◽  
Satish C. Mathur ◽  
Keya Roy ◽  
Ramadhar Singh
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field
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