2,3,5,6,-Tetraalkoxy-1,4-benzoquinones and structurally related tetraalkoxy benzene derivatives: synthesis, properties and solid state packing motifs

Abstract

A general synthesis of 2,3,5,6-tetraakloxy-1,4-benzoquinones 1 from 1,2,4,5-tetraalkoxynenzones 3 is reported. IR analysis (1a–e), the single crystal X-ray analysis of 2,3,5,6-tetramethoxy-1,4-benzoquinone 1a and semi-empirical calculations (AM1, 1a) show that the 1,4-benzoquinone skeleton possesses a merocyanine-type distortion. The solid state packing motifs of 1 are markedly affected by alkoxy chain length. For 1a, Weak C–H ⋯ O interactions and reduction of unfavourable dipole–dipole interactions are important for intermolecular organization, whereas for 2,3,5,6-tetradecyloxy-1,4-benzoquinone [1e, wide angle X-ray diffaraction (WAXD)] the close packing principle of the alkyl chains dominates. In both cases the results show that interplanar overlap is improved with respect to 1,4-benzoquinone 8. To deepen our insight into the effect of alkoxy chain length on solid state packing motifs, single crystal X-ray structures of methoxy and decyloxy derivatives of the structurally related compounds 1,4-diacetoxy-2,3,5,6-tetraalkoxybenzenes 2a and e, and e, and 1,2,4,5-tetraalkoxynenzenes 3a and e were analysed. Compounds 1e, 2e and 3e bearing decyloxy chains, posses board-like molecular structures which stack parallel along the a-axis as a result of alkyl chain interactions.