SUBSTITUENT EFFECTS ON THE HYDROGEN BONDS IN ALCOHOL*AMINE COCRYSTALS. James H. Loehlin, Department of Chemistry, Wellesley College, Wellesley, MA 02181, USA

Alcohol*amine cocrystals provide a unique system in which to study hydrogen bonding, since each N and O atom participates in three independent hydrogen bonds. Each oxygen atom acts as a donor in one hydrogen bond and as acceptor in two others to separate nitrogen atoms. The amines form the complementary two donor and one acceptor hydrogen bonds to neighboring oxygen atoms. We have grown a series of cocrystals between 1,4-phenylene diamine and various phenols and a complementary series between hydroquinone and anilines.

Our present study involves structures in which the H atom at the para position on the phenol or aniline in the parent compound [Loehlin, Etter, Gendreau & Cervasio (1994), Chem. Mater., 6, 1218-1221 and K.J.Franz, Senior Honors Thesis, Wellesley College, 1995] is replaced by -CH₃, -Cl, and -phenyl. Data from our structures will be correlated with that from the published structures by Ermer and Eling [J. Chem. Soc. Perkin Trans. 2, 1994, 925] with -OH, -NH₂, -phenol and -aniline substituents in the para position on the phenol or aniline. Most of the structures have parallel networks of hydrogen bonds in a hexagonal grid with the di-functional moieties bridging between the networks. The para substituents are located between the molecular layers where they interact with similar or complementary groups on the adjacent hydrogen-bonded sheet. The steric interactions affecting the hydrogen-bond networks are almost identical, allowing correlation with models predicting substituent- induced electronic effects through the aromatic ring. In our structures, the layers are held to one another by weak van der Waals' forces.

The hydrogen bonds are oriented in a nearly ideal tetrahedral arrangement, with almost linear N***H-O or O***H-N geometry. A detailed comparison of the hydrogen bond lengths and angles will be presented for all the structures studied to date.