Hydrogen bonding probes electron density variations at the basic center in substituted alkyl benzoates: Theory and experiment

Abstract

Theoretical computations of charge density parameters are juxtaposed to experimental spectroscopic shifts induced by hydrogen bonding for a series of 21 substituted in the aromatic ring ethyl and methyl benzoates. Strong correlations between atomic charges at the proton accepting atom and the shifts of methanol O-H frequencies are established. Hirshfeld, Charge Model 5 (CM5), and natural population analysis (NPA) atomic charges are evaluated using ωB97X-D/6-311++G(3df,2pd) and MP2/6-311++G(3df,2pd) computations. The results obtained reveal the power of hydrogen bond measurements in characterizing the variations of electron densities at the proton accepting center within a series of structurally related molecules. The limits of application of the approach are outlined.

Mini-Review on Structure–Reactivity Relationship for Aromatic Molecules: Recent Advances

“… a Atomic charges evaluated using the Hirshfeld, CM5 and NPA methods from ωB97X-D/6-311++G­(3df,2pd) density functional theory computations (for references to the theoretical methods employed and the experimental Δν­(OH) exp shifts in CCl 4 solvent see ref ). b Absolute values of correlation coefficients. …”

“…The relationships between the shifts of methanol O−H stretching frequencies upon hydrogen bonding with the carbonyl basic center for a series of substituted methyl and ethyl benzoates and theoretical quantities characterizing the electron densities at the proton accepting atom were examined in recent research. 22 Four different types of atomic charges for the monomeric aromatic molecules were evaluated from ωB97X-D/6-311++G(3df,2pd) and MP2/6-311++G(3df,2pd) computations. The conductorlike polarized continuum model (CPCM) was employed in simulating the CCl 4 solvent used in recording the experimental IR spectra.…”

“…As discussed, the Δν-(OH) exp shifts characterize the overall basicity of molecules. 17 This investigation 22 goes a step further by considering the relationship between electron densities and spectroscopic shifts. The strong correlations established between the Δν(OH) exp and q O for the series of molecules considered shows that the approach adopted provides an experimental approach to assessing in a quantitative way the trend of variation of the electron density at the proton-accepting atom.…”