Substituted 2-(Dimethylamino)biphenyl-2′-carboxaldehydes as Substrates for Studying n→π Interactions and as a Promising Framework for Tracing the Bürgi-Dunitz Trajectory

The Bürgi-Dunitz trajectory traces points along the pathway of bond formation between a nucleophile and electrophile. Previous X-ray crystallographic studies of some molecules containing a nucleophilic nitrogen atom and electrophilic carbonyl group provided some initial evidence for various degrees of bond formation via initial n→π interactions. Observation of a complete set of points along the trajectory, however, has not yet been attained. In this paper, we present a DFT computational study investigating substituted 2-(dimethylamino)biphenyl-2′-carboxaldehydes as substrates for further examination of n→π interactions and as a potential framework for more complete tracing of the Bürgi-Dunitz trajectory. These compounds are particulary suitable for study because of the rotational freedom granted by the C-C bond connecting the two aromatic rings allowing the molecule to choose the degree of interaction between the two complementary groups. The extent of interaction is measured by interatomic distance, NBO second-order perturbative analysis energies, volume of transferred electron density as provided by ETS-NOCV analysis, and differences in energies between models that allow for n→π interactions and those that do not. A series of substituted biphenyls are ultimately identified as future synthetic targets that have maximum potential for providing improved tracing of the Bürgi-Dunitz trajectory.