Investigation of solute–solvent interactions in phenol compounds: accurate ab initio calculations of solvent effects on 1H NMR chemical shifts

Abstract

Accurate (1)H chemical shifts of the -OH groups of polyphenol compounds can be calculated, compared to experimental values, using a combination of DFT, polarizable continuum model (PCM) and discrete solute-solvent hydrogen bond interactions. The study focuses on three molecular solutes: phenol, 4-methylcatechol and the natural product genkwanin in DMSO, acetone, acetonitrile, and chloroform. Excellent linear correlation between experimental and computed chemical shifts (with the GIAO method at the DFT/B3LYP/6-311++G(2d,p) level) was obtained with minimization of the solvation complexes at the DFT/B3LYP/6-31+G(d) and DFT/B3LYP/6-311++G(d,p) level of theory with a correlation coefficient of 0.991. The use of the DFT/B3LYP/6-31+G(d) level of theory for minimization could provide an excellent means for the accurate prediction of the experimental OH chemical shift range of over 8 ppm due to: (i) strong intramolecular and solute-solvent intermolecular hydrogen bonds, (ii) flip-flop intramolecular hydrogen bonds, and (iii) conformational effects of substituents of genkwanin. The combined use of ab initio calculations and experimental (1)H chemical shifts of phenol -OH groups provides a method of primary interest in order to obtain detailed structural, conformation and electronic description of solute-solvent interactions at a molecular level.

An NMR Method for the Quantitative Assessment of Intramolecular Hydrogen Bonding; Application to Physicochemical, Environmental, and Biochemical Properties

“…Similar results were found with 5,3′-and 5,4′-dihydroxyflavones. Siskos et al 18 confirmed the results of Whaley et al 17 for 5,4′-dihydroxy-7-methoxyflavone (genkwanin), where separate signals are observed for the 4′-and 5-hydroxy substituents (see Table 2). …”

Nuclear Magnetic Resonance Spectroscopy Investigations of Naphthalene-Based 1,2,3-Triazole Systems for Anion Sensing

“…The highly deshielded triplet peak is an indication of the stable hydrogen bonded HF 2 − ion. This provided evidence to a deprotonation pathway in the ion-recognition process (Figures S9 and S10) [57,58].…”

Determination of Polyphenolic Phytochemicals using Highly Deshielded –OH 1H‐NMR Signals

“…The derived Δ δ /Δ Τ coefficients in DMSO‐ d 6 and acetone‐ d 6 , with the exception of the C‐5 OH of flavonoids, are in the range of −5.4 to −12.0 ppb/K. The Δ δ /Δ Τ coefficients of C‐5 OH protons are significantly smaller in absolute terms, |Δδ/ΔΤ | ≤ 3 ppb/K, than those of the other hydroxyl protons which are exposed to the solvent (Kontogianni et al , ; Siskos et al ., ). Therefore, in the temperature range 283–303 K, changes of the chemical shifts of the C‐5 OH protons are expected to be ≤0.06 ppm and, thus, negligible.…”