The title compounds, 1-chloro-3,6-dimethoxy-2,5-dimethylbenzene, (IIIa), and 1-chloro-3,6-dimethoxy-2,4-dimethylbenzene, (IIIb), both C10H13ClO2, were obtained from 2,5- and 2,6-dimethyl-1,4-benzoquinone, respectively, and are intermediates in the synthesis of ammonium quinone derivatives. The isomers have different substituents around the methoxy groups and crystallize in different space groups. In both molecules, the methoxy groups each have different orientations with respect to the benzene ring. In both cases, one methoxy group lies in the plane of the ring and can participate in conjugation with the aromatic system, while the second is almost perpendicular to the plane of the aromatic ring. The C-O-C bond angles around these substituents are also different: 117.5 (4) and 118.2 (3) degrees in (IIIa) and (IIIb), respectively, when the methoxy groups lie in the plane of the ring, and 114.7 (3) and 113.6 (3) degrees in (IIIa) and (IIIb), respectively, when they are out of the plane of the ring.