Ovchinnikov’s Rule

Ovchinnikov s Rule The lowest state of an alternant conjugated molecule will have the multiplicity associated with the Sz value of its MSAD, that is, it will be a singlet ifna = np in the MSAD, a doublet ifna = np + 1, a triplet ifna = np + 2, and so on. 

Extending Ovchinnikov s Rule to Search for Bistable Hydrocarbons... 

Use Ovchinnikov s rule to predict the preferred multiplicities for the ground states of the hydrocarbon diradicaloids displayed in Scheme 8.Ex.l... 

Encouragingly, the orbital phase predictions on ground-state spin of the alternant hydrocarbon diradicals, 1, 5, 7, and 13, are in agreement with those proposed by Borden and Davidson [64,71, 78-80], by Ovchinnikov [72], and by Radhakrishnan [49, 50]. For the non-altemant systems and hetero-derivatives, 16-20, the orbital phase theory performs as well as the Radhakrishnan s rule [49, 50]. 

Through studies exemplified by those described above, Hund s rule as a prime directive predicting HS ground states in all non-Kekule molecules was eventually ruled out. The Ovchinnikov-Klein and Borden-Davidson approaches are now frequently used to predict ground spin states for... 

In the strongly-correlated limit, when the electron delocalization (i.e. the tpq terms) becomes smaller than the electron repulsion U, an appropriate description of the lowest states is provided by the neutral VB determinants only, i.e. those in which each carbon p bears one unpaired electron in its n atomic orbital (AO, hereafter labelled 5 ). The n electron systems behaves as a pure spin system, obeying a Heisenberg Hamiltonian [22,23]. The inter-atomic delocalization, i.e. the interaction between the neutral VB distributions and the ionic ones, results in an antiferromagnetic spin coupling on each bond. One of the below-discussed rules, known as the Ovchinnikov s mle [21], has been derived from this magnetic approach. Numerous works [24] have shown the relevance of magnetic descriptions... 

An alternative stream came from the valence bond (VB) theory. Ovchinnikov judged the ground-state spin for the alternant diradicals by half the difference between the number of starred and unstarred ir-sites, i.e., S = (n -n)l2 [72]. It is the simplest way to predict the spin preference of ground states just on the basis of the molecular graph theory, and in many cases its results are parallel to those obtained from the NBMO analysis and from the sophisticated MO or DFT (density functional theory) calculations. However, this simple VB rule cannot be applied to the non-alternate diradicals. The exact solutions of semi-empirical VB, Hubbard, and PPP models shed light on the nature of spin correlation [37, 73-77]. 

The technique of complex-valued dielectric functions was originally applied to solvation problems by Ovchinnikov and Ovchinnikova [2] in the context of the electron transfer theory. They reformulated in terms of s(k, to) the familiar golden rule rate expression for electron transfer [3], This idea, thoroughly elaborated and extended by Dogonadze, Kuznetsov and their associates [4-7], constitutes a background for subsequent nonlocal solvation theories. 

---