Synthesis and P.M.R. study of 2-(2',4'-Dihydroxy-6'-methylbenzoyl)-3,6-dihydroxybenzoic acid and its methyl ethers

1975 ◽  
Vol 28 (3) ◽  
pp. 657 ◽  
Author(s):  
BW Au-Yeung ◽  
T Chan ◽  
SW Tam
Keyword(s):  
Hydrogen Bonding ◽  
Carboxylic Acid ◽  
Potassium Hydroxide ◽  
Chemical Shifts ◽  
Intramolecular Hydrogen Bonding ◽  
Dihydroxybenzoic Acid ◽  
Alcoholic Potassium Hydroxide ◽  
Intramolecular Hydrogen ◽  
Aryl Methyl ◽  
Methoxybenzoic Acid

The syntheses of 2-(2?,4?-dihydroxy-6?-methylbenzoyl)-3,6- dihydroxybenzoic acid (4) and its methyl ethers are described. Treatment of 6-hydroxy-2-(2?-hydroxy-4?-methoxy-6?-methylbenzoyl)-3- methoxybenzoic acid (8) with alcoholic potassium hydroxide gave 2- hydroxy-6-methoxy-8-methyl-9-oxoxanthene-1-carboxylic acid (9). Comparison of the p.m.r. spectra of these structurally related 2- benzoylbenzoic acids revealed that the chemical shifts of the aryl methyl and the ring protons are significantly influenced by the existence of intramolecular hydrogen bonding.

scholarly journals NMR of Natural Products as Potential Drugs

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3763
Author(s):  
Poul Erik Hansen
Keyword(s):  
Natural Products ◽  
Hydrogen Bonding ◽  
Density Functional ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Density Functional Theory Calculations ◽  
Intramolecular Hydrogen Bonding ◽  
Chemical Equilibria ◽  
Nmr Techniques ◽  
Intramolecular Hydrogen

This review outlines methods to investigate the structure of natural products with emphasis on intramolecular hydrogen bonding, tautomerism and ionic structures using NMR techniques. The focus is on 1H chemical shifts, isotope effects on chemical shifts and diffusion ordered spectroscopy. In addition, density functional theory calculations are performed to support NMR results. The review demonstrates how hydrogen bonding may lead to specific structures and how chemical equilibria, as well as tautomeric equilibria and ionic structures, can be detected. All these features are important for biological activity and a prerequisite for correct docking experiments and future use as drugs.

A carbon-13 nuclear magnetic resonance study of the basicities of aliphatic alcohols

1987 ◽  
Vol 65 (8) ◽  
pp. 1769-1774 ◽  
Author(s):  
Donald G. Lee ◽  
Kenneth J. Demchuk
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Hydrogen Bonding ◽  
Chemical Shifts ◽  
Intramolecular Hydrogen Bonding ◽  
Nuclear Magnetic Resonance Study ◽  
Slope Parameter ◽  
Magnetic Resonance Study ◽  
Linear Free Energy ◽  
Intramolecular Hydrogen

Carbon-13 nmr chemical shifts have been used to determine the basicity constants for nine alcohols. The method involves comparing the chemical shifts for carbon atoms adjacent to the site of protonation with those for carbon atoms in a more remote position. The differences in the chemical shifts (Δ values) at different acidities are then used to calculate basicity constants for the alcohols. The pKBH+ values, determined by use of the "X function" are as follows: ethanol −2.12, 1-propanol −2.12, 3-chloro-1-propanol −2.24, 2-chloroethanol −2.45, 2-bromoethanol −2.41, 2-nitroethanol −2.09, 2-methoxyethanol −1.93, 2-phenoxyethanol −1.87, and 2-propanol −2.06. The typical slope parameter, m*, is 0.17. Two linear free energy correlations are obtained: when the alcohols are considered to be a series of monosubstituted ethanols, the Hammett plot has a slope of 0.65; when they are considered to be a series of mono- and disubstituted methanols, the slope is 1.7. Alcohols bearing oxygen-containing substituents are more basic than predicted by about 0.5 pK units, presumably because their conjugate acids can be stabilized by intramolecular hydrogen bonding.

Photochemical reactions of azo compounds. X. Photochemical properties of azobenzene-2-carboxylic acids

1967 ◽  
Vol 20 (5) ◽  
pp. 929 ◽  
Author(s):  
CP Joshua ◽  
GE Lewis
Keyword(s):  
Hydrogen Bonding ◽  
Carboxylic Acid ◽  
Carboxylic Acids ◽  
Intramolecular Hydrogen Bonding ◽  
Photochemical Reactions ◽  
Azo Compounds ◽  
Neutral Compounds ◽  
Methyl Derivatives ◽  
Intramolecular Hydrogen ◽  
Derivatives Of

Two chloro and two methyl derivatives of azobenzene-2-carboxylic acid have been found to yield the corresponding derivatives of benzo[c]cinnoline-4- carboxylic acid in good yields when irradiated in 98% sulphuric acid. The question of intramolecular hydrogen bonding in relation to the properties of azobenzene-2-carboxylic acids is discussed. Infrared absorption spectra of the neutral compounds have provided confirmation of internal hydrogen bonding. Attempts to prepare the cis isomers of these azo compounds have been unsuccessful.

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