The Weakly Strained Benzene Chromophore and the Interaction Vector Model of the Secondary Transition, in Tetraline Like Molecules, in Tocopherols, Thymol, Tetrahydrocannabinol, and Canadine

Abstract

Many natural products display a benzene chromophore with simple π donating substituents such as alkyl, -OR, or -NH₂ groups. Often these molecules bear rings fused to the benzene moiety, and the strain imposed by these rings induces specific behaviours. ^1,2 The intensity of the secondary transition (towards 255 nm for the benzene molecule itself) has been a puzzling challenge during many years for the experimentalist, unless he could use sophisticated quantum approaches, unfitted to its needs. The SKLAR's vector approach has been quite interesting, but far too much qualitative. ³ It has been shown recently, using simple vector addition rules within the interaction vector model^4,5 (IVM), that it is possible to calculate the intensity of the secondary transition of the benzene chromophore in the above molecules, on a simple basis. The present work will be devoted to show how to extend the application of the IVM to other molecules displaying six membered fused rings with weak strain effects, and doing so to test the limits of the model.

Experimental intensity is given as ε_sm, the maximum of the smoothed absorption curve, as it has been defined by BALLESTER and RIERA ⁶ (the calculated value is: ε_{sm, c}). The ε_sm values given in their work are used when necessary.