HYDROGEN BONDING IN SOLUTIONS OF SUBSTITUTED ACETIC ACIDS

1961 ◽  
Vol 39 (8) ◽  
pp. 1711-1720 ◽  
Author(s):  
Leonard W. Reeves
Keyword(s):  
Hydrogen Bonding ◽  
Chemical Shift ◽  
Carboxylic Acids ◽  
Trifluoroacetic Acid ◽  
Dimethyl Formamide ◽  
Acid Solutions ◽  
Dilute Solution ◽  
Acid Proton ◽  
Solvent Molecules ◽  
Acetic Acids

The changes in chemical shift of the acid proton in some simple carboxylic acids on dilution in four solvents has been studied. The existence of chainlike hydrogen-bonded polymers in solution is suggested by the results. The association of the monomer molecules in dilute solution with donor centers in the solvent molecules is suggested from a study of the —O—H monomer stretching bond in the vapor and in two solvents. There is a difference in the behavior of acetic and trifluoroacetic acid in N-methyl and N,N-dimethyl formamide, which has been explained in terms of protonation of the amides in trifluoroacetic acid solutions.

Chemical-shift link to the Kamlet–Taft β parameter

2004 ◽  
Vol 82 (12) ◽  
pp. 1707-1711 ◽  
Author(s):  
Keith C Brown ◽  
Muhsin El-Bermani ◽  
John A Weil
Keyword(s):  
Hydrogen Bonding ◽  
Liquid Phase ◽  
Chemical Shift ◽  
Solvent Effects ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Proton Nmr ◽  
Empirical Parameter ◽  
Interesting Correlation ◽  
Solvent Molecules

In investigating liquid-phase proton NMR spectra of 2,2-dimethyl-1-(2,4,6-trinitrophenyl)hydrazine in various solvents, we have found an interesting correlation, at sufficiently low temperatures T, between the chemical-shift difference (splitting) of the picryl proton peaks, measured as f(T), and the Kamlet–Taft hydrogen-bonding basicity parameter β. The observed solvolytic effect offers a convenient way of determining and checking the value of the empirical parameter β. The phenomenon discloses that the molecular geometric configuration is affected vividly by hydrogen bonding with the surrounding solvent molecules. It follows that the internal conformation interchange taking place (in a higher T range) is not in fact solely a unimolecular property.Key words: picryl proton NMR, chemical shift, solvent effects, hydrogen bonding, Kamlet–Taft β.

Effects of Multiple Binding Sites on Studies of Hydrogen Bonding between Nitroxide Radicals and Solvent Molecules

1993 ◽  
Vol 58 (1) ◽  
pp. 47-52 ◽  
Author(s):  
Imad Al-Bala'a ◽  
Richard D. Bates
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Binding Site ◽  
Binding Sites ◽  
Hyperfine Coupling Constant ◽  
Hydrogen Donor ◽  
Complex Formation Constants ◽  
Multiple Binding Sites ◽  
Multiple Binding ◽  
Solvent Molecules

The role of more than one binding site on a nitroxide free radical in magnetic resonance determinations of the properties of the complex formed with a hydrogen donor is examined. The expression that relates observed hyperfine couplings in EPR spectra to complex formation constants and concentrations of each species in solution becomes much more complex when multiple binding sites are present, but reduces to a simpler form when binding at the two sites occurs independently and the binding at the non-nitroxide site does not produce significant differences in the hyperfine coupling constant in the complexed radical. Effects on studies of hydrogen bonding between multiple binding site nitroxides and hydrogen donor solvent molecules by other magnetic resonance methods are potentially more extreme.

scholarly journals Relevance of Hydrogen Bonds for the Histamine H2 Receptor-Ligand Interactions: A Lesson from Deuteration

Biomolecules ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 196 ◽  
Author(s):  
Mojca Kržan ◽  
Jan Keuschler ◽  
Janez Mavri ◽  
Robert Vianello
Keyword(s):  
Hydrogen Bonding ◽  
Active Sites ◽  
Density Functional ◽  
Receptor Activation ◽  
Histamine H2 Receptor ◽  
Therapeutic Practice ◽  
H2 Receptor ◽  
Ligand Interactions ◽  
Solvent Molecules ◽  
Near Future

We used a combination of density functional theory (DFT) calculations and the implicit quantization of the acidic N–H and O–H bonds to assess the effect of deuteration on the binding of agonists (2-methylhistamine and 4-methylhistamine) and antagonists (cimetidine and famotidine) to the histamine H2 receptor. The results show that deuteration significantly increases the affinity for 4-methylhistamine and reduces it for 2-methylhistamine, while leaving it unchanged for both antagonists, which is found in excellent agreement with experiments. The revealed trends are interpreted in the light of the altered strength of the hydrogen bonding upon deuteration, known as the Ubbelohde effect, which affects ligand interactions with both active sites residues and solvent molecules preceding the binding, thus providing strong evidence for the relevance of hydrogen bonding for this process. In addition, computations further underline an important role of the Tyr250 residue for the binding. The obtained insight is relevant for the therapy in the context of (per)deuterated drugs that are expected to enter therapeutic practice in the near future, while this approach may contribute towards understanding receptor activation and its discrimination between agonists and antagonists.

Tris(biimidazolato)chromium(III) as a building block for hydrogen-bonded supramolecular assemblies

2006 ◽  
Vol 84 (7) ◽  
pp. 949-959 ◽  
Author(s):  
Letitia M Gruia ◽  
Fernande D Rochon ◽  
André L Beauchamp
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Porous Material ◽  
Intermolecular Interactions ◽  
Long Range ◽  
Building Block ◽  
Benzene Molecule ◽  
Methanol Solution ◽  
Solvent Molecules ◽  
Free Material

The trischelate [Cr(H2biim)3](NO3)3 complex of 2,2′-biimidazole (H2biim) was obtained by reacting CrCl3·3THF with [Ag(H2biim)](NO3) in methanol. In the solvent-free material, each ligand forms two N-H···O bonds to a nitrate ion and generates locally neutral [Cr(H2biim)3](NO3)3 units. A methanol solvate was also obtained in which intermolecular interactions involve optimal use of the hydrogen-bonding ability of the [Cr(H2biim)3]3+ cations, NO3– anions, and methanol molecules. In both cases, there is no long-range regular organization of the complex units. Deprotonation of [Cr(H2biim)3](NO3)3 with NaOCH3 yielded neutral Cr(Hbiim)3. Its powder pattern is similar to that of Ru(Hbiim)3, suggesting that it also consists of mutually perpendicular interlocked honeycomb sheets. Recrystallization by slow diffusion of diisopropyl ether into a methanol solution yielded a porous material of composition Cr(Hbiim)3·2.6C6H14O in which superposed honeycomb sheets create infinite channels (~13 Å diameter) filled with disordered solvent molecules. A totally different structure is adopted by the solvate Cr(Hbiim)3·C6H6·2H2O, where the benzene molecule is encapsulated in a cavity created by five complex molecules.Key words: chromium, biimidazole, supramolecular, crystal structure, hydrogen bonding.

ChemInform Abstract: Synthesis of 2-Methylchromone-8-acetic Acids and 2-Methylchromone-8-carboxylic Acids.

ChemInform ◽  
2010 ◽  
Vol 32 (44) ◽  
pp. no-no
Author(s):  
S. G. Jagadeesh ◽  
G. L. David Krupadanam ◽  
G. Srimannarayana
Keyword(s):  
Carboxylic Acids ◽  
Acetic Acids
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