We have been using single-crystal X-ray diffraction to investigate the structures and properties of compounds from two families of nitrogen-containing organic compounds: the benzonitrile oxides (R-CN+-O-, R = aryl) and the benzylideneanilines (R-CH=N-R’, R = aryl). In solution, benzonitrile oxides dimerize to form three possible products: one head-to-head dimer (the furoxan) and two head-to-tail dimers (the dioxadiazine and the oxadiazole-N-oxide). We are examining the course of solid-state dimerization of benzonitrile oxides to determine which dimer is formed in the crystal and whether or not the product of solid-state dimerization can be predicted on the basis of the molecular packing arrangement of the benzonitrile oxide. We are also investigating the possibility that different dimers could be formed from different polymorphs of a given benzonitrile oxide. We have now prepared 4-chlorobenzonitrile oxide and have determined its crystal structure. Our previous work has shown that the solid-state dimerization product is the head-to-head dimer, but the closest intermolecular distances between reactive sites in this crystal are found to be between inversion-related molecules. This result is consistent with calculations indicating that the transition state leading to the head-to-head dimer is centrosymmetric. We intend to determine how the close intermolecular oxygen-halogen contact we observe in this structure might also occur in the 2- and 3-chloro isomers and influence their solid-state molecular packing and reactivity. In a parallel investigation, we are examining the role of intermolecular contacts involving halogens in establishing the crystal structures of bridge-flipped isomeric benzylideneanilines, isomers related by the reversal of the bridge (R-CH=N-R’ vs. R-N=CH-R’). To determine whether close intermolecular contacts of the type X-R-CN:…X-R-CN: occurring in both members of a bridge-flipped pair will encourage their isomorphism (identical packing arrangements), we have prepared and determined the crystal structure of 4’-cyanobenzylidene-2-bromoaniline. In this structure, space-filling considerations apparently dominate, and no nitrile/halogen contacts occur.

Effects of molecular structure on crystal structure and solid-state reactivity of some nitrogenous organic compounds

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.