Unzipping the dimer in primary amides by cocrystallization with sulfoxides

A systematic crystal engineering study was undertaken to investigate how different electronic substituents on the aromatic ring of primary aromatic amides impact the ability of the amide to cocrystallize with dibenzyl sulfoxide. Amides which cocrystallize with dibenzyl sulfoxide form 1:1 cocrystals containing a discrete N-H•••O=S supramolecular synthon as well as the well-known C(4) amide chain. The combination of these two synthons gives rise to linear chains of amide molecules, with each amide molecule capped by one sulfoxide molecule. Thus, the R2₂(8) dimer typically seen for primary amides is no longer present in these cocrystals. The influence of electronic effects of substituents on the amide is similar to that observed for acids in cocrystals.