Molecular structure and intramolecular hydrogen bonding in 2-hydroxybenzophenones: A theoretical study

Abstract

The intramolecular hydrogen bonding (IHB) in a series of 3-, 4-and 5-substituted 2hydroxybenzophenone (HBP) is studied using density functional theory calculations. All calculations are performed at the B3LYP level, using 6-311++G** basis set. To understand the substitution effects on the nature of IHB and the electronic structure of the chelated ring system, the vibrational frequencies, 1 H chemical shift, topological parameters, natural bond orders and natural charges over atoms involved in the chelated ring of HBP and its derivatives were calculated. The Wiberg bond indices and the natural charges over atoms involved in the chelated ring have been computed using the natural bond orbital (NBO) analysis. The computations were further complemented with an atoms-in-molecules (AIM) topological analysis to characterize the nature of the IHB in the considered molecules. Several correlations between geometrical parameters, 1 H NMR chemical shift and topological parameters with the IHB strength are obtained.

Relationships between NMR shifts and interaction energies in biphenyls, alkanes, aza‐alkanes, and oxa‐alkanes with X─H…H─Y and X─H…Z (X, Y = C or N; Z = N or O) hydrogen bonding

“…Correlations between hydrogen‐bond strength and spectroscopic parameters go back to Badger and Bauer's work of 1937 on the vibrational spectra of hydrogen‐bonded complexes between alcohols and various solvents . NMR spectral shift enhancement is recognised as a criterion of hydrogen bonding, and many correlations between shifts and different measures of the hydrogen‐bond strength, not only in complexes but also related to intramolecular interactions, have been proposed. Such correlations have been used to infer hydrogen‐bond strengths or distances from spectroscopic data.…”

“…Hydrogen‐bond energies, enthalpies, binding energies, and heats of formation, determined by various approaches, have been frequently used, as well as correlations with bond length, it being tacitly or explicitly accepted that energy and bond length are correlated. In the context of QTAIM analysis, when there is a BCP associated with the hydrogen bond, other properties, such as the electron density, ρ, its Laplacian, ∇ 2 ρ, and the potential‐energy density, V, have been exploited . Clearly, many of the parameters that can be used for the correlation of NMR shifts are interrelated, and there is nothing to be gained by doing all the possible correlations.…”

Tetrafluoroborate and Hexafluorophosphate Ions are not Interchangeable: A Density Functional Theory Comparison of Hydrogen Bonding

“…Positive values for the ∇ 2 ρ BCP therefore suggest that the charge is depleted at the BCP and the electronic charge is not shared, indicating the presence of closed‐shell interactions, such as ionic and hydrogen bonding . The typical value of the Laplacian for a hydrogen bond ranges from 0.023–0.139 a.u., however, the value can be more positive when an O−H bond donor is involved ,. The values for the water and methanol complexes are within that range, but those of phenol are larger than the upper limit, which may be attributed to resonance‐assisted hydrogen bonding …”

“…The results of AIM analysis in Table are also consistent with the calculated energies listed in Table , suggesting that the hydrogen bonds within the H 3 O + complexes are the strongest, as indicated by the high ρ BCP . In fact, the calculated ρ BCP for the dimers are greater than the upper limit, which suggests that the H‐bonds formed are partially covalent in nature ,. The ∇ 2 ρ BCP for the H 3 O + complexes are greater than the upper limit, however, presumably due to charge‐assisted (cation‐anion) hydrogen bonding, consistent with a mixture of covalency and electrostatic stabilization in the hydrogen bonding.…”

2, 2′‐Dihydroxybenzophenones and Derivatives. Efficient Synthesis and Structure Endoscopy by DFT and NMR. Credentials as Potent Antiinflammatory Agents.

“…Substituted ortho hydroxybenzophenones, are ubiquitous in naturally occurring and synthetic compounds with important biological activities . Their structure and the inherent intramolecular H bonding have been the subject of extensive theoretical investigations . The ortho ‐hydroxy diaryl ketone entity in many biologically active compounds and natural products makes it a privileged structure in medicinal chemistry and a synthesis target .…”