Two polymorphs of 5-cyclohexyl-5-ethylbarbituric acid and their packing relationships with other barbiturates

Abstract

Polymorph (Ia) (m.p. 474 K) of the title compound, C12H18N2O3, displays an N—H...O=C hydrogen-bonded layer structure which containsR66(28) rings connecting six molecules, as well asR22(8) rings linking two molecules. The 3-connected hydrogen-bonded net resulting from these interactions has thehcbtopology. Form (Ib) (m.p. 471 K) displays N—H...O=C hydrogen-bonded looped chains in which neighbouring molecules are linked to one another by two differentR22(8) rings. Polymorph (Ia) is isostructural with the previously reported form II of 5-(2-bromoallyl)-5-isopropylbarbituric acid (noctal) and polymorph (Ib) is isostructural with the known crystal structures of four other barbiturates.