Three-dimensional structures of 1-acyl-5-hydroxypyrazolidines

It was shown by x-ray diffraction analysis and PMR spectroscopy that 1-acyl-5-hydroxy- and -5-hydrazinopyrazolidines have a conformation with an axial orientation of the functional group attached to the C(₅) atom. The 1-salicylyl derivatives constitute an exception: in methanol solutions they exist in a conformation with an equatorial hydroxy group, whereas in dimethylformamide (DMF) the ring undergoes partial opening to give the corresponding -hydrazido aldehydes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1242–1247, September, 1985.     

Acid-base characteristics of 2-acyl-3(5)-hydroxyisoxazolidines in a hydrogen bond

In solution hydroxyisoxazolidines form intermolecular hydrogen bonds. For 3-hydroxyisoxazolidines the proton acceptor is the oxygen atom of the hydroxyl group, and for the 5-hydroxy compounds it is the cyclic oxygen atom. These compounds are close to phenol with respect to the relative acidity in the hydrogen bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 818–820, June, 1990.     

1-Aroyl-2-benzyl-5-hydroxypyrazolidines

The PMR spectral data show that 1-aroyl-2-benzyl-5-hydroxypyrazolidines are preferentially present in cyclic form in solution, while the proportion of the linear form increases to 50% in the gaseous phase, according to mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1199–1203, September, 1990.     

Reaction of 5-hydroxypyrazolidines with hetarylamines

The reaction of 1-acetyl-5-hydroxypyrazolidines with heterocyclic compounds, the amino group of which has an aniline or amidine character, is regioselective and results in the formation of the corresponding hetarylaminopyrazolidines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1204–1206, September, 1990.     

Synthesis of 1-acyl-5-aryl biurets

Fourteen new 1-acyl-5-aryl biurets were synthesized by the reaction of aryl ureas with acylisocynantes. The latter was obtained from acyl chloride and lead cyanate in dichloromethane, using pyridine as catalyst. The structures of compounds 3a-n were confirmed by IR,1H NMR and MS spectra.     

Interaction of 5-hydroxypyrazolidines with Ch-acid compounds

The interaction of I-acetyl-2 phenyl-5-hydroxypyrazolidine with carbonyl compounds on the surface of acidic aluminum oxide results in the formation of products in which the hydroxyl group has been replaced by the residue of the carbonyl compound. It has been shown that derivatives of ß-dicarbonyl compounds, under the conditions of the reaction, may undergo subsequent conversions in which one of the carbonyl-containing residues is split off.M. V. Lomonosov Moscow State University, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 483–489, April, 1994. Original article submitted January 31, 1994.     

Palladium-catalysed amination of 2-acyl-1-alkyl-5-bromopyrroles

The first intermolecular C-N bond-forming reactions between substituted 2-bromopyrroles and primary and cyclic secondary amines were performed using Pd₂(dba)₃ as catalyst with BINAP as the ligand. The aminations proceeded in the presence of NaO^tBu at 80-100 °C in 31-93% yields.     

Tetrazoles. 9. Acid-base properties of 5-substituted tetrazoles

The basicities of series of 5-R-tetrazoles in aqueous solutions of sulfuric acid were studied by UV and PMR spectroscopy. The pK_BH ⁺ values of these compound correlate with the _p substituent constants. The transmission factor of the p-phenylene ring (' = 0.23) was calculated from the ratio of the reaction constants for protonation of substituted 5-phenyltetrazoles and 5-R-tetrazoles. A linear dependence between the pK_a values and the pK_BH ⁺ values of 5-substituted tetrazoles was established.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 559–562, April, 1981.     

2-alkyl-5-aryltetrazoles as hydrogen bond acceptors

The dissociation constants of the H-complexes formed by 2-alkyl-5-aryltetrazoles and p-fluorophenol in carbon tetrachloride (pK _HB 0.9–1.3) were determined by Fourier-transform IR spectroscopy. 2-Alkyl-5-aryltetrazoles were found to act as medium-strength hydrogen bond acceptors comparable with diazines. The thermodynamic parameters of the equilibrium formation of H-complex with 2-isopropyl-5-phenyltetrazole were determined. The electronic nature of substituents in the tetrazole ring only slightly affects the pK _HB values of tetrazoles.     

Room temperature ICl-induced dehydration/iodination of 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles. a selective route to substituted 1-acyl-4-iodo-1H-pyrazoles

A number of new functionally substituted 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles have been prepared in moderate to excellent yields from the corresponding 2-alkyn-1-ones. The resulting dihydropyrazoles undergo dehydration and iodination in the presence of ICl and Li2CO3 at room temperature to provide 1-acyl-4-iodo-1H-pyrazoles.     

Defining the bond energy of a strong hydrogen bond

Based on a recent definition of hydrogen-bond energy the hydrogen bond in [HCOO…H…F]^? is weaker than that in [F…H…F]^?, although the former still ranks as a very strong hydrogen bond.     

Acid-base properties of 1,2,5-oxadiazoles. 1. Methylfurazans

The basicities of 3-methyl-4-R-furazans (R = H, CH₃, C₂H₅, n-C₃H₇, NH₂ NHAcOCH₃, I, COOH, and NO₂) were investigated by PMR spectroscopy. It is shown that they are weak bases, the protonation of which is described by the H_A acidity function. Relationships between the chemical shifts of the protons of the methyl group and the R ° constants and the p _aBH ^K + and the M ° constants of the substituents were found.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 35–37, January, 1981.     

Acid-base properties of poly(1-vinylazoles) in aqueous solution

The interaction of poly(1-vinylimidazole) and poly(1-vinyl-1,2,4-triazole) with HCl and alkalies in aqueous and water-salt solutions was investigated by potentiometric titration, viscosimetry, ¹H and ¹³C NMR, and UV spectroscopy. The effect of the nature and concentration of low-molecular counterions was found. The interaction of poly(1-vinylazoles) with the acid results in the protonation of the azole cycle. The interaction of poly(1-vinylazoles) with alkalies is stipulated by the capability of the pyridine N atom of forming a coordination bond with the metal ion and that of the unsaturated pi-system of the heterocycle of coordinating with the anions.     

Charge transfer theory and vibrational properties of the hydrogen bond

An extension of Mulliken's charge transfer theory leads to the following correlations: the change in the transition moment of the X—H stretching vibration with the enhancement of dipole moment, and the displacement of the X—H stretching frequency with the ionization of donors. Experimental data for a number of hydrogen-bonded complexes are in accord with these predictions.     

The role of intermolecular hydrogen bond on dielectric properties in hydrogen-bonded material 5-bromo-9-hydroxyphenalenone: theoretical investigation

Dielectric properties of the hydrogen-bonded material, 5-bromo-9-hydroxyphenalenone (C(13)H(7)O(2)Br; BrHPLN), are investigated theoretically by means of electronic structure calculations and Monte Carlo simulations. The density functional calculations of BrHPLN crystals have revealed that the polarization per one molecule can be about 1.7 times larger than that of the isolated monomer. It is also found that there exists significant electron density (0.01 e bohr(-3)) in an intermolecular C-H···O region, which, together with the interatomic distances of 2.39 ? for H···O and 3.34 ? for C···O, suggests the existence of intermolecular weak hydrogen bonding that may enhance the molecular polarization. The induced polarization effects in various intermolecular configurations are evaluated with the Fragment Molecular Orbital method. In addition to the π-π stacking interactions, two types of "in plane" intermolecular weak hydrogen-bonding configurations are found to affect the molecular dipole moment most significantly. These effects are efficiently included in a Monte Carlo simulation method in terms of "dipole corrections" as functions of both the intermolecular arrangements and the intramolecular proton configurations. The application to the dielectric phase transition of a BrHPLN crystal shows that the dipole corrections almost double the transition temperature, toward better agreement with experiments, and qualitatively affect the temperature dependence of the dielectric constant. Discussions are given to support that the results will remain adequate and consistent even after explicit inclusion of the quantum tunneling effects.     

1JCH correlates with alcohol hydrogen bond strength

The strength of the H-bond donation by alcohols is reflected in the carbon-hydrogen bond of the H-C-O-H functional group. The one-bond 13C-1H spin-spin coupling constant of hexafluoroisopropanol (HFIP) correlates with the strength of the H-bond in various HFIP-amine complexes with a slope of approximately -0.2 Hz in 1JCH per approximately 1 kJ mol(-1) increase in the H-bond enthalpy. The decrease in 1JCH is attributed to an increased overlap of the H-bonding sigma orbital with the antibonding sigma orbitals of the vicinal C-H bonds.     

Acid-base properties of sulfoxylate ion

The kinetics of the reaction of sulfoxylate with methylviologen monocation and oxygen in aqueous alkaline solutions was studied. From the results obtained, the pK _m of the SO₂H^? ion was determined for the first time.