Frontier Configuration Theory of Spin Selection

The spin selection problem revolves about the determination of the sign and magnitude of the energy difference between two different spin states and a given geometry, g, and a given number of electron pairs, n. For our purposes, g can be either a Hiickel AO (HAO) or Mbbius AO (MAO) geometry. 

If we restrict our attention to the lowest energy singlet (S) and triplet (T) states of M-l/M, M/M, and M+l/M species, we have  

The and H.j matrix elements for singlet and triplet PC s have the forms shown in Table 1. Accordingly, Asp(g,n) can be expressed as follows  

Where X. . is the parity invariant overlap term, L. . is the overlap term responsible for parity stereoselection,and I is the stabilization energy due to the interaction of the PC s. 

in systems which can be represented by normal Lewis structures in which electrons are coupled to bond pairs and lone pairs, AX is always positive. 

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Chapter 17. Frontier Configuration Theory of Spin Selection. 

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