THE INTERACTION VECTOR MODEL AND THE SECONDARY TRANSITION OF THE PHTHALIC-ANHYDRIDE CHROMOPHORE

The interaction vector model(1-3) (IVM) has been used to calculate on a very simple basis, and a good accuracy, the intensity of the seconda ry transition of the benzene chromophore of more than 80 molecules. In this paper we shall study the phthalic anhydride chromophore. Such a molecule is interesting in the frame of the IVM, since it displays a f ive membered ring, fused to the benzene ring, which imposes to that be nzene ring a strong strain and a classical conjugation. No previous mo lecule displaying these two joined effects, which could cancel their r espective influence on intensity, has been studied. The phthalic anhyd ride molecule will allow to study these effects and test the IVM in su ch a case. Furthermore, the whole molecules which have been studied ti ll now display only pi donating substituents. So, before studying the phthalic anhydride molecule, it is necessary to determine the values o f the IVM parameters necessary for that study; that is to say : to stu dy the behaviour of pi withdrawing substituents such as -CO(2)R.