Conformational stabilisation of a 2-pyridyl imide by n→π* interaction in solid state

In recent studies, n→π* interactions featuring nucleophilic pyridine have been investigated using Fourier transform microwave spectroscopy and high-level theoretical computations. Examples of n→π* of this type in the solid state, however, are limited. The norbornene-based 2-pyridyl imide <b>1</b> is a compound that can adopt two conformers, in which the pyridyl nitrogen is either <i>syn</i> or <i>anti</i> to the norbornane bridge. It would be expected that the <i>syn</i> conformation of imide <b>1</b> would be more favourable, as indicated in a previous computational study. Here, tandem crystallographic and additional computational studies provide evidence that the otherwise unfavourable <i>anti</i> conformer of imide <b>1</b> becomes favoured upon stabilisation by an n→π* interaction in the solid state.