Two- and three-dimensional stacking of chiral alcohols

An investigation of bulk single crystals and crystalline monolayers at the air-water interface of secondary alcohols bearing 16 and 17 carbons has been carried out in order to investigate their molecular packing. These "simple" chiral molecules can be seen as model systems; therefore, their studs might provide broader knowledge of how chirality affects the molecular arrangement. The bulk racemic mixtures exhibit racemate organization, i.e., ordered mixtures of left and right enantiomers, with a head to head packing, whereas the pure enantiomers present a head to tail arrangement. The former type of motif has been reported for many amphiphilic molecules, whereas the latter is more rare, In two dimension, all compound,,. pure enantiomer, racemic mixtures, as well as other mixtures, present a hexagonal rotator phase with lattice parameters close to 5 A. The rotational motion suggests the formation of a two-dimensional solid solution. However, upon heating, monolayers of 2-heptadecanol present a peculiar evolution. For mixtures of the two enantiomers with ratios between 1:1 and 2:1, the hexagonal phase transforms to a centered rectangular one, due to an inclination of molecules of about 10degrees with respect to the vertical. The loss of hexagonal symmetry is attributed to the formation of a racemate.