W0330

Molecular Substituents as Intermolecular Switches. A.M. Beatty* and C.B. Aakeröy, *Dept. of Chemistry, Univ. of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, IN 46556 USA.

By looking at the three-dimensional arrangement of small molecules, the structure of the crystal rather than the structure of the molecule, Crystal Engineers have been able to identify intermolecular interactions that recur with surprising regularity. For example, by now it is clear that some hydrogen-bonding substituents can participate in self-complementary interactions (e.g. the hydrogen bonded carboxylic acid dimer) or may serve as partners to other hydrogen-bonding functionalities (e.g. the carboxylic acid-carboxamide dimer). Etter¹ has suggested that the interactions are hierarchical (the best hydrogen bond donor will interact with the best hydrogen bond acceptor). The questions are: Can we use substituents to influence the intermolecular outcome? Can we make stronger hydrogen bond donors or acceptors electronically? Can we switch hydrogen bond donors or acceptors “on” and “off” using electron donating or electron withdrawing substituents? We have tried to answer these questions by determining the crystal structures of a series of related nicotinic acid and nicotinamide molecules.

¹ M.C. Etter, Acc. Chem. Res. 1990, 23, 120.