A conformational study of [3.3](3,5)pyridinophane

Abstract

A variable temperature 1H NMR study of the [3.3](3,5)pyridinophane indicated that the syn(chair/chair) is more stable than syn(chair/boat) by 0.2 kcal/mol in solution, whereas the trimethylene bridges show disorder even at −150 °C in the solid state. A transition state search by ab initio MO calculations suggested two competitive conformational changes for syn(chair/chair)– syn(chair/boat) conversion via a bridge wobble or a ring inversion in the [3.3](3,5)pyridinophane.