Relative influence of noncovalent inter­actions on the melting points of a homologous series of 1,2-dibromo-4,5-dialk­oxy­benzenes

Crystal structures are presented for two members of the homologous series of 1,2-dibromo-4,5-di­alk­oxy­benzenes, viz. those with decyl­oxy and hexa­decyl­oxy substituents, namely 1,2-dibromo-4,5-bis(decyl­oxy)­benzene, C₂₆H₄₄Br₂O₂, (II), and 1,2-dibromo-4,5-bis(hexa­decyl­oxy)­benzene, C₃₈H₆₈Br₂O₂, (III). The relative influences which halogen bonding, [pi]-[pi] stacking and van der Waals inter­actions have on these structures are analysed and the results compared with those already found for the lightest homologue, 1,2-dibromo-4,5-dimeth­oxy­benzene, (I) [Cukiernik, Zelcer, Garland & Baggio (2008). Acta Cryst. C64, o604-o608]. The results confirm that the prevalent inter­actions stabilizing the structures of (II) and (III) are van der Waals contacts between the aliphatic chains. In the case of (II), weak halogen C-Br...(Br-C)' inter­actions are also present and contribute to the stability of the structure. In the case of (III), van der Waals inter­actions between the aliphatic chains are almost exclusive, weaker C-Br...[pi] inter­actions being the only additional inter­actions detected. The results are in line with commonly accepted models concerning trends in crystal stability along a homologous series (as measured by their melting points), but the earlier report for n = 1, and the present report for n = 10 and 16, are among the few providing single-crystal information validating the hypothesis.