The Crystal Structure of Pyrazinic Acid

Abstract The crystal structure of pyrazinic acid has been determined by X-ray diffraction method. The crystal is orthorhombic, space group Pna21, a=11.352, b=7.363, c=6.454Å, and Z=4. The structure was solved by inspecting the sharpened Patterson map. The final R value is 6.4% for all observed reflections. The molecule does not take a zwitter ion, but a neutral form. The dimensions of the pyrazine ring are close to those of pyrazine. Each molecule is joined, through the O–H···N hydrogen bond with distance of 2.669 Å, to two neighboring molecules forming the chain. These chains are linked by the weak C–H···O hydrogen bond to form the sheet parallel to the (0 0 1) plane. This hydrogen bonding scheme is quite similar to that of nicotinic acid. The hydrogen bonding type found in nicotinic acid is considered energetically favored more than that found in picolinic acid.