Crystal and molecular structure of 2-amino-5-butyl-3-ethyl-6-methyl-4(3H)-pyrimidinone

The structure of 2-amino-5-n-butyl-3-ethyl-6-methyl-4(3H)-pyrimidinone (1) has been studied by X-ray diffraction and ab initio calculations at the HF/6-31G* level. X-ray analysis established that 1 exists as the amino-oxo tautomer (AO) in the solid state, in good agreement with the ab initio results. Crystals of 1 are tetragonal (space group P42/n); the unit cell dimensions are a = 17.074 Å, b = 17.074 Å, c = 8.809 Å, α = β = γ = 90°. The 4-pyrimidinone ring is essentially planar in the crystal, the amino nitrogen and the carbonylic oxygen being located in the plane of the ring. The 2-amino-5-n-butyl-3-ethyl-6-methyl-4(3H)-pyrimidinone molecules are linked by strong N-H ⋯ O intermolecular hydrogen bonds from the NH2 group of one molecule to the C=O group of an adjacent molecule (N-H ⋯ O distance: 2.88 Å).