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 Pna2₁, but less satisfactory refinement can also be achieved in Pbcn), the mol­ecules are linked into chains by two short C—H...π 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.