THE MORPHINE CHROMOPHORE - THE INTERACTION VECTOR MODEL AND THE INTENSITY OF THE 285-NM TRANSITION

The interaction vector model(1) (IVM) enables to calculate the intensi ty of the secondary transition of the benzene chromophore (towards 255 nm for the benzene molecule itself) using simple vector addition rule s, when the chromophore bears alkyl, -OR, and -NH2 substituents. Furth er, the IVM has been designed to take into account the perturbations i nduced by the strain of rings fused to the benzene moiety, on intensit y.(2) The present work will be devoted to show how the IVM can be brou ght into play to analyze the origin of intensity in the morphine molec ule, a more complex chromophore (Figure 1), which displays a surprisin gly low intensity owing to the fact that there are two -OR substituent s and two fused rings. In this molecule the rings fused to the benzene moiety are also fused one another, distorting the molecule(3, 4) (the se rings will be named : superfused rings). Thus, they can strongly pe rturb the other interaction with the chromophore. In order to understa nd how to adapt the IVM to that case one will study some strained mole cules (Figure 2), some of them having superfused rings. Experimental i ntensity is given as epsilon(sm), the maximum of the smoothed absorpti on curve, as it has been defined by BALLESTER and RIERA (5) (the calcu lated value is : epsilon(sm,c)). The epsilon(sm,) values given in thei r sm work will be used. Depending on the sources, and on solvents, int ensity of the secondary transition of the morphine like chromophore ra nges from: epsilon(sm) = 1510 to epsilon(sm) = 1800 [for ethylmorphine chlorhydrate(6): epsilon(sm) = 1800 (methanol), epsilon(sm) = 1660 (w ater), epsilon(sm) = 1680 (water + HCl 0.1 M), E epsilon(sm) = 1520 (w ater + KOH 0,1 M); for morphine itself 1510-1610 (7)]