The Interaction Vector Model and the Intensity of the Secondary Transition of the Benzene Chromophore in Strained Natural Molecules: Sesamol,Melacacidin, Tetrahydropapaverolin,Renifolin, Pterocarpin,Peltogynol

A method (the New Vector Model : NVM) designed to approach the intensity of the secondary transition of the benzene chromophore with-CH3 and-OR substituents, has been recently published ¹ This method is based on MNDO calculations. It has been applied to strained chromophores with fused rings, ² assuming that it is possible to take into account the incidence of strain on intensity in introducing a strain vector in the vector scheme used to calculate the transition moment vector. In another step it has been derived a much simpler method which avoids the quantum calculations. It can be brought into play using graphically simple vector addition rules. ³ This method is based on a new concept : the interaction vector (underneath, the method is called the Interaction Vector Model : IVM). It has been designed to study alkyl and-OR substituents, since we are mainly involved in the study of natural products and many natural products display such substituents. This IVM has not been designed to take into account the perturbations induced by the strain on intensity. The present work is devoted to the adaptation of the IVM to strained benzene chromophores. It is given several examples on the way it can be used on strained natural molecules.