The crystal structures of four di-meth-oxy-benzaldehyde isomers.

The crystal structures of four di-meth-oxy-benzaldehyde (C9H10O3) isomers, namely the 2,3-, 2,4-, 2,5- and 3,5- isomers, are reported and compared to the previously reported crystal structures of 3,4-di-meth-oxy-benzaldehyde and 2,6-di-meth-oxy-benzaldehyde. All di-meth-oxy-benzaldehyde mol-ecules in the crystal structures are nearly planar. The largest deviation (1.2 Å) from the aromatic plane is found for one of the meth-oxy groups of 2,3-di-meth-oxy-benzaldehyde. Upon rapid cooling of 3,4-di-meth-oxy-benzaldehyde and 3,5-di-meth-oxy-benzaldehyde, a metastable polymorph is formed. The crystal studied for the 3,5- isomer was refined as a two-component twin.