Amide interactions in chlorinated solvents

The experimental pKHB hydrogen-bond (HB) basicity scale and the corresponding DeltaH[symbol: see text]HB enthalpic scale of nitrogen compounds are extended and analysed in light of simple theoretical descriptors using the B3LYP density functional method and a medium-size basis set (6-31+G(d,p)).The selected training set includes 59 monofunctional unhindered nitrogen bases for which homogeneous and accurate experimental pKHB and DeltaH[symbol: see text]HB data have been determined by means of the association equilibrium of the bases with a reference hydrogen-bond acid, 4-fluorophenol, in CCl4. The three hybridisation states encountered in the nitrogen atom, sp, sp2 and sp3, are equally represented in this data set. A proper estimation of their experimental enthalpy (DeltaH[symbol: see text]HB) is directly attainable from the theoretical enthalpy of the complexation reaction with hydrogen fluoride (DeltaH[symbol: see text](HF)). However, a second parameter is required to calculate with good accuracy the experimental free energy of association represented by pKHB. About 99% of the variance of the pKHB scale is described by a bilinear equation using the minimum electrostatic potential (Vs,min) of the monomer in addition to the interaction energy (D0(HF). The equations are tested for an external set of 99 additional compounds including very different nitrogen bases such as ortho-substituted pyridines, polyazines and azoles.Theoretical calculations give a reliable estimation of hydrogen-bond basicity provided that the populations of the different isomers of the bases are taken into account by using the Boltzmann law, and that a specific halogen-bond interaction with the solvent CCl4 is considered for polybasic molecules.The pKHB scale can thus be extended to important classes of species experimentally inaccessible in CCl4, to polynitrogen compounds and to molecules of biological significance.

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Are solvent effects important for intramolecular C—H···O⁻ hydrogen bonding interactions?

Wang

Shao

Yan

et al. 2018

J of Physical Organic Chem

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Oxygen atoms are located at the center of the symmetrical rectangles formed by four ortho t-butyl carbon-hydrogen (C-H) bonds for the conformational inflexible 2,6-di-t-butyl-4-substituted phenoxide anions, in which the nonbonded O···H and O···C distances are all significantly shorter than sums of the related van der Waals' radii. Noncovalent interaction (NCI) and atoms in molecules (AIM) analysis reveal that the oxygen atom can form four equivalent intramolecular C-H···O − hydrogen bonds (approximately 3.0 kcal/mol) regardless of size and polarity of the para-substituents, implying that each phenoxide anion is stabilized by approximately 12 kcal/mol C-H···O − hydrogen bonding interaction. The C-H···O − hydrogen bonding stabilizations are strongly supported by acidity augmentation of approximately 1.6 pK units (approximately 40 times) for introduction of two bulky t-butyl groups into the ortho positions of 4-substituted phenols (G = H, Me, t-Bu, MeO, and NO 2 ) in dimethyl sulfoxide solution. Furthermore, solvents with largely varying polarity show negligible effects on the intramolecular C-H···O − hydrogen bonding strengths.KEYWORDS atoms in molecules (AIM), C-H···O − hydrogen bonding interactions, noncovalent interaction (NCI), solvent effects and 2,6-di-t-butyl-4-substituted phenoxide anions

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Amide interactions in chlorinated solvents

Cited by 13 publications

References 10 publications

Physical and Theoretical Aspects of 1H‐Pyrroles

Physical and Theoretical Aspects of 1H‐Pyrroles

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Are solvent effects important for intramolecular C—H···O⁻ hydrogen bonding interactions?

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Amide interactions in chlorinated solvents

Cited by 13 publications

References 10 publications

Physical and Theoretical Aspects of 1H‐Pyrroles

Physical and Theoretical Aspects of 1H‐Pyrroles

A Theoretical Evaluation of the pKHBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Are solvent effects important for intramolecular C—H···O− hydrogen bonding interactions?

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A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Are solvent effects important for intramolecular C—H···O⁻ hydrogen bonding interactions?