Solid-state and Calculated Electronic Structure of 4-Acetylpyrazole

The crystal structure of 1-(1H-pyrazol-4-yl)ethanone (commonly known as 4-acetylpyrazole; C5H6N2O) was determined from single-crystal X-ray data at 173 K: monoclinic, space group P2(1)/n (no. 14), a = 3.865(1), b = 5.155(1), c = 26.105(8) angstrom, beta = 91.13(1)degrees, V = 520.0(2) angstrom(3) and Z = 4. The adjacent molecules assemble into a wave-like ribbon structure in the solid state, linked by strong intermolecular N-H center dot center dot center dot N hydrogen bonds between the pyrazole rings and a weak C-H center dot center dot center dot O=C hydrogen bond involving the carbonyl group. The ribbons are stacked in the solid state via weak pi interactions between the pyrazole rings.