Hydrogen bonding in urea

The hydrogen bond consisting of a hydrogen atom positioned asymmetrically between a nitrogen and an oxygen atom (N-H . . .O) plays a central role in the structure and functionality of proteins and amino acids. The urea crystal is a simple system in which such a hydrogen bond exists. We have measured Compton profile anisotropies in crystalline urea which reveal subtle modulations linked to this chen-deal bond. The data presented here have sufficient statistical accuracy to isolate features arising from intermolecular interaction which is weak in urea and consequently difficult to detect experimentally.