Similarities and differences in the structures of 5-bromo-6-hydroxy-7,8-dimethylchroman-2-one and 6-hydroxy-7,8-dimethyl-5-nitrochroman-2-one

Abstract

The title compounds, C11H11BrO3, (I), and C11H11NO5, (II), respectively, are derivatives of 6-hydroxy-5,7,8-trimethylchroman-2-one substituted at the 5-position by a Br atom in (I) and by a nitro group in (II). The pyranone rings in both molecules adopt half-chair conformations, and intramolecular O-H···Br [in (I)] and O-H···O(nitro) [in (II)] hydrogen bonds affect the dispositions of the hydroxy groups. Classical intermolecular O-H···O hydrogen bonds are found in both molecules but play quite dissimilar roles in the crystal structures. In (I), O-H···O hydrogen bonds form zigzag C(9) chains of molecules along the a axis. Because of the tetragonal symmetry, similar chains also form along b. In (II), however, similar contacts involving an O atom of the nitro group form inversion dimers and generate R2(2)(12) rings. These also result in a close intermolecular O···O contact of 2.686 (4) Å. For (I), four additional C-H···O hydrogen bonds combine with π-π stacking interactions between the benzene rings to build an extensive three-dimensional network with molecules stacked along the c axis. The packing in (II) is much simpler and centres on the inversion dimers formed through O-H···O contacts. These dimers are stacked through additional C-H···O hydrogen bonds, and further weak C-H···O interactions generate a three-dimensional network of dimer stacks.