Ring and nitrogen inversion in a flexible highly symmetrical molecule: The conformations of 1,3,7,9,13,15,19,21-octaazapentacyclo[19,3,1,1, 3,7,1 9,13,1 15,19

Abstract

The possible conformations of the title compound and their modes of interconversion via ring and nitrogen inversion processes are delineated. At high temperatures (> +80°) the 1H NMR spectra are consistent with time averaged D 4th symmetry and rapid ring and nitrogen inversion. At lower temperatures ( ca. −10°) the time-averaged symmetry if D 2d and inversion of the 6-membered rings is frozen out, nitrogen inversion remaining rapid. The free energy of activation for the total inversion of all four 6-membered rings is 13·5 kcal mole −1, higher than in similar monocyclic systems. This higher energy is a reflection of the multiple ring inversion pathway required for total inversion of all the 6-membered rings.