Some Current Statements Concerning a and n Electrons

In Chapt. 2 we have recalled how a and it orbitals can be defined in terms of a rigorous theory and what the notions of a and it electrons actually mean. In Chapt. 3 we have introduced the a—it separation and discussed its justification and limitations. If the a—it separation is valid, then an effective Hamiltonian for the it electrons can be constructed into which the a electrons enter only via the effective potential created by their charge distribution. 

Of course, the basic question is why stress the distinction between a and it orbitals and the cr—n separation Is this point of view really useful, or is it just a trivial by-product of the quantum-mechanical treatment A partial answer has already been given in Chapt. 1 to some extent, the notion that there are two classes of electrons associated with quite different molecular properties is suggested by experimental evidence These two classes have been identified with the a and it electrons defined in the preceding sections, and this has resulted in a number of conclusions regarding both the theoretical and experimental differences between a and it electrons. These conclusions can be summarized in the following rather familiar statements  

None of these statements is rigorously true, but all hold grosso modo. In the following sections, we shall comment on them in more detail. 

---