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