Secondary interactions in two related terphenyl derivatives: 2',5'-dimethyl-p-terphenyl and 2',5'-bis(bromomethyl)-p-terphenyl.

In 2',5'-dimethyl-p-terphenyl, C20H18, which displays pseudosymmetry (the true space group is Pna2(1), but less satisfactory refinement can also be achieved in Pbcn), the molecules are linked into chains by two short C-H...pi interactions to the centroid of the central ring. In 2',5'-bis(bromomethyl)-p-terphenyl, C20H16Br2, the polar CH2Br groups cause molecules to aggregate via C-H...Br and Br...Br interactions, forming a layer structure, in which the phenyl rings project outwards from the central, more polar, region.