Monocentric perturbations

We now assume that t-bond energies of the conjugate acids (e.g., 436) are independent of the position of the N-atom (i.e., , is constant). This is reasonable if we consider the cations as monocentric perturbations of 1-naphthol. Equation (8) now reduces to the form... 

Two conjugated systems can differ in any of three respects. The atoms involved may be different the topology of overlap may be different and the total number of conjugated atoms may be different. We can then express any overall difference as a sum of individual perturbations of three kinds. First, monocentric perturbations, in which a given atom is altered or replaced by some other atom second, intramolecular perturbations, in which we alter the connectivity of the conjugated system and third, intermolecular perturbations, in which two smaller conjugated systems unite tjo form a larger system. 

The first type of perturbation, a monocentric perturbation, is seen in the protonation of pyridine (1) to pyridinium ion (2) ... 

The second type of perturbation, i.e., intramolecular union, can be treated in a manner exactly similar to that for the monocentric perturbations. We are concerned here with a process in which two conjugated atoms k and /)... 

We have so far considered only single perturbations, i.e., monocentric perturbations due to a change of one atom and intramolecular and intermolec-ular union through a single pair of atoms. The results can, however, be extended to multiple perturbations. 

As we have now developed a general theory of 7c-electron structure in AHs, we can extend this to heteroconjugated molecules using the results for monocentric perturbations of Section 3.5. 

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