Correlations of NHN hydrogen bond energy with geometry and 1H NMR chemical shift difference of NH protons for aniline complexes

Abstract

In this computational work, we propose to use the NMR chemical shift difference of NH2 protons for 1:1 complexes formed by aniline and nitrogen-containing proton acceptors for the estimation of the hydrogen bond energy and geometry (N⋯H and N⋯N distances). The proposed correlations could be applied to other aromatic amines as well, in a gas phase, a solution, or a solid state, for both inter- and intramolecular hydrogen bonds. We considered a set of 21 complexes with the NHN hydrogen bond without proton transfer, including hydrogen bonds from weak to medium strong ones (2–21 kcal/mol), with neutral or anionic bases and with sp3 and sp2 hybridized nitrogen proton acceptors. For each complex apart from direct hydrogen bond energy calculation, we have tested several other ways to estimate the energy: (a) using a correlation between NH stretching band intensity and hydrogen bond energy and (b) using correlations between electron density properties at (3, −1) bond critical point (quantum theory of atoms in molecules analysis) and hydrogen bond energy. Besides for the studied type of complexes, we obtained refined linear correlations linking the local electron kinetic (G) and potential (V) energy densities with the hydrogen bond energy.

Quantitative decomposition of resonance‐assisted hydrogen bond energy in β‐diketones into resonance and hydrogen bonding (π‐ and σ‐) components using molecular tailoring and function‐based approaches

“…However, the values of the V local potential energy of the electrons at the critical point of the H‐bond, which is the most popular descriptor of H‐bond, were not presented in these papers by Rusinska‐Roszak. The V values were widely used for estimation of the H‐bond energy by means of the Espinosa's equation and its modified versions . For this reason, we had to calculate this parameter additionally.…”

How Strong is Hydrogen Bonding to Amide Nitrogen?

“…The obtained values of Δ δ (NH) were used for the estimation of the hydrogen bond energy (Table ) . For most cations 5H + , this energy does not exceed 3 kcal ⋅ mol −1 .…”

“… [a] calculated according to correlation equation, [b] the value obtained under −40 °C, substance exist in two conformations (Figure S68, S69).…”

Benchmark calculations of intramolecular hydrogen bond energy based on molecular tailoring and function‐based approaches: Developing hybrid approach

“…To disclose this issue, the shortcomings of each method should be weighted. Main drawback of estimated equations from the FBA method is the uncertainties in the calibration coefficients included in them . To the best of our knowledge, the disadvantages of the MTA method have not yet reviewed as they do not lie on the surface.…”