Hydrogen Bonding in Urea

The hydrogen bond consisting of a Hydrogen atom positioned asymmetrically between a Nitrogen and Oxygen atom (O...H-N) plays a central role in the structure and functionality of proteins and amino acids. In particular, the Urea crystal is perhaps the simplest system in which such a hydrogen bond exists. We have measured Compton profile anisotropies in crystalline Urea which reveal subtle modulations which can be linked to the details of this chemical bond. The data presented here has sufficient statistical accuracy to allow us to identify contributions arising from the covalent character of the O...H-N.