Hydrogen bonding and thermodynamic properties of (R,S)- and (R)-alanine-based selector

We report on structural investigation of homochiral and heterochiral alanine-based selector 4-butylamino-N-[1-(3,5-dimethyl-phenylcarbamoyl)-ethyl]-3,5-dinitrobenzamide (I) preformed by X-ray structure analysis and thermo-optical analysis. The topologies of hydrogen bonding of racemate crystals and the homochiral crystals are significantly different and affect their thermodynamic stabilities. The heterochiral rac-I crystal is characterized by high temperature and entropy fusion due to the compact packing of the molecules of opposite chirality (hydrogen bonded RS pairs). On the contrary, packing of homochiral molecules is less compact and crystals reveal low thermodynamic stability related to conformational flexibility.