The conformations of oxidized and reduced iso-alloxazine have been examined by a molecular orbital method, PRDDO (partial retention of diatomic differential overlap). The angle θ of fold about the N.N line of the central ring is zero for the planar oxidized form, but a bend of θ=10° requires only 2 kcal/mol. On the other hand, the reduced form is nonplanar (θ~15°), and the barrier for reversal of this bend is 4 kcal/mol, comparable with that in simple amines. Molecular properties and reactivity are interpreted in terms of charge and orbital distributions, and localized molecular orbitals have been derived by the method of Boys.
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