AB-INITIO STUDY OF THE C6-C7 CONFORMATION OF RETINAL MODEL SYSTEMS

Ab initio calculations have been performed on model compounds of retin al and retinal derivatives, beta-ionone, beta-ionone Schiff base and p rotonated Schiff base and the corresponding hydrocarbon, to study the ring orientation as a function of the heteroatom and the state of prot onation. Two 6-s-cis derived conformations are shown to exist in all f our compounds. Stable close to planar 6-s-trans conformations were obt ained for the protonated Schiff base and for the ketone only.