Absolute rate constants for the reactions of terr-butoxyl and triplet benzophenone, with a series of di-tert-amines have been obtained via laser flash photolysis. These diamines have in common the feature that the nitrogen centers are in the backbone of an aliphatic eight-membered ring at positions 1 and 5. A modest rate enhancement is observed, particularly for 1 in its H-abstraction reaction with tert-butoxyl, which may be explained by the operation of a stereoelectronic effect. From thc absorption maxima of the radical cations of these diamines (produced quenching acetophenone triplets), information concerning the conformations of the eight-membered rings may be inferred. It is concluded that these radical-cations are stabilized by relatively strong through-space bonding interactions between the two nitrogen centers.
IntroductionThe study of medium-ring (so-called mesocyclic) systems has provided chemists with a number of surprising results. In particular, heteroatom-substituted eight-membered rings are peculiar. 1,s-Dithiacyclooctane shows appreciable S-S interaction as evidenced by a splitting of 0.43 eV in its photoelectron (PE) spectrum (1). 1,4-Dithiacycloheptane, 13-dithiacyclononane, and 1,6-dithiacyclodecane each shows negligible S-S interaction (