In-line proximity effects in extended 7-azanorbornanes. 2. A major reduction of N-inversion barriers in symmetrically flanked systems

Through-space compression effects from a pair of flanking (sentinel) groups X are shown to cause a flattening of the bridging nitrogen in symmetricall y fused 7-azanorbornanes which is evaluated by a substantial reduction of t he nitrogen inversion barrier as measured by low-temperature H-1 NMR spectr oscopy. This effect is attributed to destabilization of the ground state of the amine.