1.2- and 1.3-Dithiolium ions

The 1,2- and 1,3-dithiolium ions (1 and 2) are unsaturated five-membered ring cations in which each of the two ring sulfur atoms can contribute a free pair of Zpn electrons to the mesomeric bond system. Thus both systems possess a potential aromatic sextet, and are therefore iso-7r-electronic with the tropylium ion (3), from which they... 

The methods and problems of quantum mechanical calculations on the electronic structures of -heterocyclic compounds in general, and of the 1,2- and 1,3-dithiolium ions in particular, have already been discussed in detail by Zahradnik in Volume 5 of this series.1 We can therefore confine the present discussion to the essential conclusions drawn from these theoretical studies. It should, however, be pointed out that, insofar as they relate to the 1,2-dithiolium ion, these are largely a priori calculations. 

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