Barriers to nitrogen inversion in six-membered rings. Ring and nitrogen inversion in some methylene bridged bisheterocycles

Abstract

A complete temperature dependent line shape analysis of 2,2′-bistetrahydro-1,2-oxazinylmethane and coalescence temperature measurements on 2,2′-bis-3,6-dihydro-1,2-oxazinylmethane, 2,2′-bis-1,2-oxazolidinyimethane and 3,3′-bistetrahydro-1,3-oxazinylmethane are reported. Joining the nitrogen atoms in the two heterocyclic rings via a methylene bridge has a negligible effect upon the ring inversion barrier, but substantially lowers the nitrogen inversion barrier. The relevance of these results to the current controversy over the barrier to nitrogen inversion in six-membered rings is discussed.