Theoretical study of conformation and dynamic behaviour of [3.3]orthocyclophane and heterocyclic analogues

Both the conformational equilibria and the dynamic behaviour of N,N′-di-substituted 3,12-di-aza-[3.3]orthocyclophane (R = H, COCH3, COPh, tosyl) were calculated by the semi-empirical PM3 method and at the ab-initio level of theory (HF 6-31G∗) in the light of inconsistent previous experimental results. The preferred conformer proved to be generally the chair form (anti-periplanar) and the exchange phenomena, which could be studied by dynamic NMR spectroscopy, result from the ring interconversional process and the restricted rotation about the exo-cyclic partial C,N double bond.