posted on 2012-09-11, 00:00authored byJacob
W. G. Bloom, Rajesh K. Raju, Steven E. Wheeler
XH/π interactions (e.g.: CH/π, OH/π,
etc.) are
ubiquitous in chemical and biochemical contexts. Although there have
been many studies of substituent effects in XH/π interactions,
there have been only limited systematic studies covering a broad range
of substituents. We provide a comprehensive and systematic study aimed
at unraveling the nature of aryl substituent effects on model BH/π,
CH/π, NH/π, OH/π, and F/π interactions (e.g.:
BH3···C6H5Y, CH4···C6H5Y, etc.) based
on estimated CCSD(T)/aug-cc-pVTZ interaction energies as well as symmetry-adapted
perturbation theory (SAPT) results. We show that the impact of substituents
on XH/π interactions depends strongly on the identity of the
XH group, and the strength of these effects increases with increasing
polarization of the XH bond. Overall, the results are in accord with
previous work and follow expected trends from basic physical principles.
That is, electrostatic effects dominate the substituent effects for
the polar XH/π interactions (NH/π, OH/π, and FH/π),
while dispersion effects are more important for the nonpolar BH/π
and CH/π interactions. The electrostatic component of these
interactions is shown to correlate well with Hammett constants (σm), while accounting for the dispersion component requires
consideration of molar refractivities (MR) and interaction distances
concurrently. The correlation of the dispersion component of these
interactions with MR values alone is rather weak.