Hydrogen bonding as a probe of electron density Variations: Substituted pyridines

An approach for experimental assessment of the trend of variations of the electron density at the basic center for series of substituted pyridines, based on the shifts of infrared O-H stretching frequencies of selected proton donating species upon hydrogen bonding with the pyridine derivatives [delta v(OH)(exp)], is validated. Strong correspondence between theoretically evaluated atomic charges (Hirshfeld, CM5) and the electrostatic potential for the pyridine nitrogen in the monomeric derivatives and spectroscopic data for the delta v(OH)(exp) shifts (ref. 7) is established. The spectroscopic shifts correlate also excellently with the rate constants for quaternization of substituted pyridines with ethyl iodide. The omega B97X-D/6-311++G(3df,2pd) method is used in the computations, conducted in the present research.