Molecular orbital method resonance

The electronic structure of dichorodiphenylplumbane was calculated by the SCF-MS (self-consistent field multiple scattering) molecular orbital method and compared to that of dichlorodiphenylstannane. The results suggest that one has to look for 35C1 NQR (nuclear quadrupole resonance) frequencies of dichorodiphenylplumbane in the 5-6 MHz region1613. 

A In this exercise we will combine valence-bond and molecular orbital methods to describe the bonding in the SO3 molecule. By invoking a 7t-bonding scheme, we can replace the three resonance structures for SO3 (shown below) with just one structure that exhibits both cr-bonding and delocalized n--bonding. 

Qualitatively, the resonance picture is often used to describe the structure of molecules, but quantitative valence-bond calculations become much more difficult as the structures become more complicated (e.g., naphthalene, pyridine, etc.). Therefore the molecular-orbital method is used much more often for the solution of wave equations.5 If we look at benzene by this method (qualitatively), we see that each carbon atom, being connected to three other atoms, uses sp1 orbitals to form a bonds, so that all 12 atoms are in one plane. Each carbon has a p orbital (containing one electron) remaining and each of these can overlap equally with the two adjacent p orbitals. This overlap of six orbitals (see Figure 2.1) produces six new orbitals, three of which (shown) are bonding. These three (called it orbitals) all occupy approximately the same space.6 One of the three is of lower energy than... 

I feel that the greatest advantage of the theory of resonance, as compared with other ways (such as the molecular-orbital method) of discussing the structure of molecules for which a single valence-bond structure is not enough, is that it makes use of structural elements with which the chemist is familiar. The theory should not be assessed as inadequate because of its occasional unskillful application. 11 becomes more and more powerful, just as does classical structure theory, as the chemist develops a better and better chemical intuition about it. 

THE RESONANCE AND MOLECULAR-ORBITAL METHODS AND THEIR APPLICATIONS. PERICYCLIC REACTIONS... 

The Resonance and Molecular-Orbital Methods and Their Applications. Pericyclic Reactions (a)... 

During the early years at McGill University, Whitehead s group concentrated on experimental nuclear quadrupole resonance spectroscopy123 and a variety of n- and all-valence electron semiempirical molecular orbital methods.124 His recent interests have included topics as diverse as density functional theory125 and related topics,126 and molecular models of surfactants. 

Molecular orbital methods have been used in conjunction with spectroscopic data (infrared (IR), Raman, nuclear magnetic resonance (NMR)) to solve spectra and to identify unstable intermediates <1998JA5005, 2004ICA1920, B-2003MI329>. These applications are discussed in the relevant sections (see Section 2.21.3). 

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