Crystal Structures of Two 4-Alkyl-8-hydroxyquinolines

4-Methyl- (1) and 4-ethyl-8-hydroxyquinoline (2) crystallize from a mixture of diethyl ether and chloroform in the triclinic space group P1¯. X-ray analysis reveals that both compounds form discrete molecular dimers stabilized by intermolecular O-H∙∙∙N and C-H∙∙∙O hydrogen bonds, resulting in R22(5) cyclic synthons. This pattern of hydrogen bonds is further stabilized by intramolecular O-H∙∙∙N bonds so that the quinoline nitrogen atom acts as a bifurcated binding site. The dimers exhibit a planar geometry and arrange into layer-like structures held together by π∙∙∙π stacking and van der Waals forces. While the fundamental bonding motifs are similar, the increased steric demand of the ethyl group in compound 2 induces a shift in the crystallographic orientation of the layers and alters the degree of π-overlap compared to the methyl-substituted analogue 1.