Conversely, in the crystalline conformation, this planarity is broken as the O-H bond is orientated almost orthogonally to the carbonyl oxygen. This conformational change allows the hydrogen to form hydrogen bonds with a neighbouring pyridine group, but at the cost of a large intramolecular penalty. It therefore seems that the rigid-body assumption breaks down for systems that contain hydrogen bonding, and that the flexibility of the polarised hydrogen should be taken into account to model these systems accurately.