State correlation diagrams application

VALENCE BOND STATE CORRELATION DIAGRAM APPLICATION TO PHOTOCHEMICAL REACTIVITY... 

Some Guidelines for Quantitative Applications of the Valence Bond State Correlation Diagram Model... 

S. S. Shaik, E. Canadell, J. Am. Chem. Soc. 112, 1446 (1990). Regioselectivity of Radical Attacks on Substituted Olefins. Application of the State-Correlation-Diagram (SCD) Model. 

On the basis of the state correlation diagram depicted in Figure 1, which connects the different stereoisomers of the pentacoordinate fragment [Rh(NH3)4Cl] +, Vanquickenbome etal. infer the main characteristics of the complicated photochemical mechanism in [Rh(NH3)4Cl2]+ and related complexes. This work gave the first evidence that the formulation of electronic selection rules was underlying the photosubstitution mechanism in d and d complexes. In principle, this idea was applicable to any complex with any coordination number. However, at this stage the... 

Figure 6. Schematic of the state correlation diagram for the concerted addition of molecular oxygen to a diene. The electronic configurations for states of the (O2 + diene) complex are indicated on the left (state of O2 in the complex given in brackets). States of the cyclic peroxides with their appropriate electronic configurations are on the right in order of increasing energy. Dashed curves indicate the primitive correlations obtained by straightforward application of symmetry and spin restrictions. Solid curves indicate final correlations obtained by using the additional information contained in the orbital correlation...

Attacks on Substituted Olefins. Application of the State-Correlation-Diagram (SCD) Model. 

The application of correlation diagrams to photochemical processes goes back to the early work of Laidler and Shuler (1951). More recently, Longuet-Higgins and Abrahamson (1965) showed how orbital-symmetry correlations may be converted into state-symmetry correlations. Here the fundamental consideration is that states of the same symmetry do not cross, i.e. the result is an avoided crossing, while states of different symmetry do cross. The principles involved are illustrated in Fig. 19 for the dimerization of... 

One of the most important applications of correlation diagrams concerns the interpretation of the spectral properties of transition-metal complexes. The visible and near ultra-violet spectra of transition-metal completes can generally be assigned to transitions from the ground state to the excited states of the metal ion (mainly d-d transitions). There are two selection rules for these transitions the spin selection rule and the Laporte rule. 

The BOVB method does not of course aim to compete with the standard ab initio methods. BOVB has its specific domain. It serves as an interface between the quantitative rigor of today s capabilities and the traditional qualitative matrix of concepts of chemistry. As such, it has been mainly devised as a tool for computing diabatic states, with applications to chemical dynamics, chemical reactivity with the VB correlation diagrams, photochemistry, resonance concepts in organic chemistry, reaction mechanisms, and more generally all cases where a valence bond reading of the wave function or the properties of one particular VB structure are desirable in order to understand better the nature of an electronic state. The method has passed its first tests of credibility and is now facing a wide field of future applications. 

Predictions can be made about the suitability of different system trajectories on the basis of orbital symmetry conservation rules (207). The most suitable trajectory is an approximation to the reaction path of the reaction under study. The rules can also yield information about the possible structure of the activated complex. The correlation diagram technique has been improved in a series of books by Epiotis et al. (214-216). The method is based on self-consistent field-configuration interaction or valence bond (SCF-CI or VB) (including ionic structures) wave functions. Applications on reactions in the ground states as well as in the excited electronic states are impressive however, the price to be paid for the predictions seems to be rather high. 

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