Infrared and Nuclear Magnetic Resonance Spectroscopic Study of Secondary Amide Hydrogen Bonding in Benzoyl PABA Derivatives (Retinoids)

Abstract

Attenuated total reflection (ATR) Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) data are used to characterize the hydrogen bonding of the secondary amide N-H group of several structurally similar benzoyl derivatives of p-aminobenzoic acid esters (retinoids) in chloroform solution. The amide N-H can form intermolecular hydrogen bonds to several proton acceptors in these molecules or it can form an intramolecular hydrogen bond to a fluorine or oxygen atom in some of the molecules. The concentration dependence of the solution N-H infrared absorption bands is used to determine the formation of intramolecular and/or intermolecular H-bonds. Proton NMR spectra were obtained from deuterated chloroform solutions and the sec-amide N-H resonance was assigned for each compound. The downfield shift in the N-H resonance is correlated to intramolecular H-bond formation. Also, the NMR spectra of fluorine-containing compounds provide J(F-H) through-space coupling values. Using infrared and NMR data, the relative intramolecular hydrogen bond strengths (N-H...F or N-H...O) of the compounds are approximately ranked.

Genetic profile of second primary tumors and recurrences in head and neck squamous cell carcinomas

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Excess Infrared Absorption Spectroscopy and its Applications in the Studies of Hydrogen Bonds in Alcohol-Containing Binary Mixtures

“…Hydrogen bonds play a very important role in determining condensed phase structures and governing their properties. [1][2][3][4] Of the different methods available to study hydrogen bonding, infrared (IR) spectroscopy is a good one because of its sensitivity towards these bonds and the availability of the instruments. In principle, infrared spectra contain very rich information concerning hydrogen bonds, as well as other weaker molecular interactions.…”

Competing HB acceptors: an extensive NMR investigations corroborated by single crystal XRD and DFT calculations

“…9d), whose value is similar to those observed for other reported molecules. 45,46,[48][49][50][51][52] All these in-depth NMR studies leads to the conclusion that the N-H/X interactions are inuenced by strong pC]O/H HB, which is also reected in the shielding of NH 1 proton and reduced value of 1h J FH in the molecule 2. These narrations suggest that the competitive equilibrium between N-H/X and pC]O/H-N type HBs debilitate with each other and is the possible reason for the shielding of NH 1 proton in the molecules 2 and 3 compared to 1.…”