Phenolic hydrogen-bonded protons

The major conclusion which was reached from the work of Jarret and Saunders was that intramolecularly hydrogen-bonded protons generally give values of (p below the value for a similar proton which is not involved in an intramolecular hydrogen bond. For example, a value of (p of 0.77 was obtained for the hydrogen-bonded site in the maleate ion [12] compared to 0.94 for acetic acid. The value for the phthalate ion [10] was higher, (p = 0.95. The value of (p = 0.95 was obtained for the salicylate ion [22] in comparison to the result for phenol, tp = 1.13. 

The NMR data confirm and amplify the IR data hydrogen-bonded protons are presented from phenolic and carboxylic groups in the coal and phenol groups added with the chemically combined phenol. The monoaromatic content (of fractions A and B especially) is high, also because of added phenol, but two-ring aromatic material also is present in all fractions (even triaromatic in C), which must have come from the original coal. The aliphatic material observed in the IR spectra of A, B, and C now is seen to consist principally of methylene bridges and short, branched aliphatic chains (a- and P-methyl predominate). 

The dipole moments wctc related to hydrogen bond strength and to the ability of the proton acceptors (compounds with phosphoryl and carbonyl groups) to associate with phenol. Hydrogen bonded complexes of pyridines, quinolines and acridine with phenol are studied, in carbon tetrachloride, by dipole moment measures . Dipole moments of the complexes were related to the ability of the acceptors to associate with phenol and with their basicity. Hydrogen bonds may either reinforce the dipole moments of the resultant of the group moments or may oppose the dipole moment direction, depending on the nature of the acceptor. 

The fact that divalent metal ions, the vanadyl ion, and their chelates, do not catalyze the hydrolysis forms [Ll and [IV] to an appreciable extent is in accord with the proposed mechanism, since coordination of the phosphate group by the metal ion would be prevented or greatly reduced by the presence of two protons. Accordingly metal ion catalysis by Cu and VO ions increases in effectiveness as the number of protons on the substrate is successively reduced. Such behavior would not be expected if transfer of a hydrogen-bonded proton from the carboxyl group to the phenolic ester oxygen were the only pathway for the reaction. Metal ion catalysis of the hydrolysis of [V], [VI],. and [VII] was not measured because of the formation of a solid phase in the presence of Cu and VO ions. 

Obviously, this shift implies the self-association of DMSO. Further frequency shifts to even lower wave numbers (1050-1000 cm " ) are observed in both aprotic polar and protic solvents. In aprotic solvents such as acetonitrile and nitromethane, the association probably takes place between the S—O bond of DMSO and the —C=N or the —NOz group in the molecules by dipole-dipole interaction as shown in Scheme 331,32. Moreover, the stretching frequency for the S—O bond shifts to 1051 cm 1 in CHC13 and to 1010-1000 cm -1 in the presence of phenol in benzene or in aqueous solution33. These large frequency shifts are explained by the formation of hydrogen bonds between the oxygen atom in the S—O bond and the proton in the solvents. Thus, it has been... 

Hydrogen bonding 5, occurs when a proton-acceptor molecule (primary and secondary amines, and sulfoxides) interacts with a proton-donor molecule (alcohols, carboxylic acids, and phenols). 

The proton-acceptor capability of some 2-acetylselenophenes in dilute sulfuric acid has been determined by the 1H NMR method.97 With phenol as proton donor, hydrogen-bond formation can be studied using IR spectroscopy as the analytical method.98 Intramolecular hydrogen-bond formation... 

A low field shift of proton signals of the OH-group in A-(salicylidenephenyl-amine-A-oxides H-12.7-13.6 ppm) indicates the presence of an intramolecular hydrogen bond. The value of this shift depends on the pK value of the parent phenol (400). While studying solvation effects of 11 NMR spectra in a-(2-hydroxy-l-phenyl)-A-(4-substituted-phenyl)nitrones, a Koppel-Palm three-parameter correlation was detected (401). 

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