Spectral characteristics of the IR?(OH) and?(NH+) bands of H-complexes of carboxylic acids and nitrogen bases with a strong hydrogen bond and with proton transfer

1975 ◽  
Vol 23 (3) ◽  
pp. 1225-1228 ◽  
Author(s):  
V. P. Glazunov ◽  
A. A. Mashkovskii ◽  
S. E. Odinokov
Keyword(s):  
Hydrogen Bond ◽  
Proton Transfer ◽  
Carboxylic Acids ◽  
Spectral Characteristics ◽  
Strong Hydrogen Bond ◽  
Nitrogen Bases

Solvent-mediated pseudo-quadruple hydrogen-bond motifs in three lamotrigine–carboxylic acid complexes

2013 ◽  
Vol 69 (10) ◽  
pp. 1164-1169 ◽  
Author(s):  
Balasubramanian Sridhar ◽  
Jagadeesh Babu Nanubolu ◽  
Krishnan Ravikumar
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Carboxylic Acid ◽  
Proton Transfer ◽  
Antiepileptic Drug ◽  
Carboxylic Acids ◽  
Solvent Interactions ◽  
Partial Transfer ◽  
Quadruple Hydrogen Bonding ◽  
Quadruple Hydrogen Bond

Lamotrigine, an antiepileptic drug, has been complexed with three aromatic carboxylic acids. All three compounds crystallize with the inclusion ofN,N-dimethylformamide (DMF) solvent,viz.lamotriginium [3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazin-2-ium] 4-iodobenzoateN,N-dimethylformamide monosolvate, C9H8Cl2N5+·C7H4IO2−·C3H7NO, (I), lamotriginium 4-methylbenzoateN,N-dimethylformamide monosolvate, C9H7Cl2N5+·C8H8O2−·C3H7NO, (II), and lamotriginium 3,5-dinitro-2-hydroxybenzoateN,N-dimethylformamide monosolvate, C9H8Cl2N5+·C7H3N2O7−·C3H7NO, (III). In all three structures, proton transfer takes place from the acid to the lamotrigine molecule. However, in (I) and (II), the acidic H atom is disordered over two sites and there is only partial transfer of the H atom from O to N. In (III), the corresponding H atom is ordered and complete proton transfer has occurred. Lamotrigine–lamotrigine, lamotrigine–acid and lamotrigine–solvent interactions are observed in all three structures and they thereby exhibit isostructurality. The DMF solvent extends the lamotrigine–lamotrigine dimers into a pseudo-quadruple hydrogen-bonding motif.

1H NMR studies of proton transfer in Schiff base and carboxylic acid systems

1990 ◽  
Vol 68 (10) ◽  
pp. 1909-1916 ◽  
Author(s):  
Hoa Le-Thanh ◽  
D. Vocelle
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Hydrogen Bond ◽  
Schiff Base ◽  
Proton Transfer ◽  
Carboxylic Acids ◽  
Proton Nuclear Magnetic Resonance ◽  
Nmr Studies ◽  
H Nmr ◽  
Mineral Acids ◽  
Rapid Equilibrium

When the unconjugated Schiff base, isobutylidene isopropylamine (2), reacts with acids such as the mineral acids HCl, HBr, and HI, or the carboxylic acids trichloroacetic, monochloroacetic, and propionic acid, in CDCl3, several complexes are formed. In this study, 1H NMR allows us to differentiate between several possibilities. With the mineral acids, only 1:1 structures are seen and the chemical shift of the [Formula: see text] proton varies according to the strength of the hydrogen bond between the protonated Schiff base and its counterion. With the carboxylic acids, 1:1 and 1:2 structures are present in rapid equilibrium. In the presence of an excess of acid, protonation of the Schiff base increases considerably. Extrapolation of the results is given in terms of the molecular mechanism of vision. Keywords: protonation, proton nuclear magnetic resonance, proton transfer, rhodopsins, Schiff base.

A mechanism for efficient proton-transfer catalysis. Intramolecular general acid catalysis of the hydrolysis of 1-arylethyl ethers of salicylic acid

1999 ◽  
Vol 77 (5-6) ◽  
pp. 792-801 ◽  
Author(s):  
Sarah E Barber ◽  
Kathryn ES Dean ◽  
Anthony J Kirby
Keyword(s):  
Hydrogen Bond ◽  
Salicylic Acid ◽  
Proton Transfer ◽  
Acid Catalysis ◽  
Enzyme Mechanism ◽  
Base Catalysis ◽  
Strong Hydrogen Bond ◽  
Cooh Group ◽  
Tert Butyl ◽  
General Acid

The tert-butyl (1) and 1-arylethyl ethers (2) of salicylic acid are hydrolyzed with efficient general acid catalysis by the ortho-COOH group. The half-life of the neutral COOH form of the tert-butyl ether is 15.2 min at 39°, and the estimated acceleration by the COOH group of 2, X = Me, Y = H is 2.13 × 105. The salicylate leaving group from 2 (X = Me, Y = H) has an effective pKa of 2.9, compared with a nominal pKa of 8.52. Analysis of substituent effects in both arylethyl and leaving groups provides the most detailed available mechanistic insight into a reaction involving efficient intramolecular proton-transfer catalysis. The mechanism is very different from classical general acid-base catalysis. Proton transfer takes place very rapidly within a developing strong hydrogen bond, and though an integral part of the C—O cleavage process is practically uncoupled from it. "Strategic delay" of the proton-transfer step, relative to C—O cleavage, makes a significant contribution to efficiency by setting up the conditions for the formation of the strong, intramolecular hydrogen bond.Key words: catalysis, carboxyl, hydrogen bond, proton transfer, enzyme mechanism.

Pressure Dependence of the Proton Transfer Equilibrium in Hydrogen Bonded Complexes

1986 ◽  
Vol 41 (1-2) ◽  
pp. 225-229 ◽  
Author(s):  
Mariusz Maćkowiak ◽  
Piotr Kozioł ◽  
Jan Stankowski
Keyword(s):  
Hydrogen Bond ◽  
Proton Transfer ◽  
Pressure Dependence ◽  
Pressure Coefficient ◽  
Nitrogen Bases ◽  
Single Well ◽  
Double Well Potential ◽  
Bonded Complexes ◽  
Hydrogen Bonded

35Cl NQR measurements were carried out on complexes of pentachlorophenol with nitrogen bases as a function of pressure (up to 300 MPa) and of temperature. It is shown that the sign and magnitude of the pressure coefficient of the 35Cl NQR frequency is related to the degree of proton transfer. An anomaly in the pressure coefficient of ν (35Cl) has been observed near 50% of the proton transfer in the hydrogen bond. This anomaly is discussed assuming that the proton transfer equilibrium is pressure dependent. The fact that the transition from the double-well potential of the hydrogen bond to the single-well potential occurs in the critical manner is also taken into account.

Exploring zero-point energies and hydrogen bond geometries along proton transfer pathways by low-temperature NMR

1999 ◽  
Vol 77 (5-6) ◽  
pp. 943-949 ◽  
Author(s):  
Sergei N Smirnov ◽  
Hans Benedict ◽  
Nikolai S Golubev ◽  
Gleb S Denisov ◽  
Maurice M Kreevoy ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Chemical Shift ◽  
Proton Transfer ◽  
Isotopic Fractionation ◽  
Zero Point ◽  
Strong Hydrogen Bond ◽  
Zero Point Energy ◽  
Acid Base ◽  
Point Energy ◽  
Fractionation Factors

We have followed by NMR the zero-point energy changes of the hydrogen bond proton in 1:1 acid-base complexes AHB triple bond {A—H···B <-–> Aδ-···H···Bδ+ <-–> A-···H—B+} as a function of the proton position between A and B. For this purpose, the isotopic fractionation factors K between the acid-base complexes AHB + Ph3COD···B –><- ADB + Ph3COH···B, where AH represents a variety of acids and B represents pyridine-15N, were measured around 110 K, using a 2:1 mixture of liquefied CDClF2-CDF3 as solvent. As under these conditions the slow hydrogen bond exchange regime is reached, the values of K could be obtained directly by integration of appropriate proton NMR signals. Using the valence-bond order concept established previously by crystallography, the fractionation factors and corresponding zero-point energy changes (ΔZPE) are related in a quantitative way to the hydrogen bond geometries, the 1H chemical shift of the hydrogen bond proton, and the pyridine-15N chemical shift. The K values are related in a quasi-linear way to the chemical shifts of the hydrogen bond proton, where the slope depends on whether the proton is closer to oxygen or nitrogen. In the region of the strongly hydrogen-bonded quasi-symmetric complexes, which are characterized by a strong hydrogen bond contraction, the variation of K is very small in spite of substantial proton displacements.Key words: NMR, isotopic fractionation, hydrogen bonding, acid-base complexes, proton transfer, geometric isotope effects.

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