Molecular Structure of Complexes with Bifurcated Hydrogen Bond: I. N-(4-Methyl-2-nitrophenyl)acetamide

According to the results of HF/6-31G* and B3LYP/6-31G* nonempirical calculations, N-(4-methyl- 2-nitrophenyl)acetamide in the synperiplanar and antiperiplanar conformations gives stable complexes with protophilic solvents, which are stabilized by bifurcated (three-center) hydrogen bond. The complexes are characterized by (1) opposite variations of the interatomic distances and angles corresponding to intra- and intermolecular components of the bifurcated hydrogen bond, (2) extension of the intramolecular component and a more pronounced shortening of the intermolecular component with increase in the strength of the three-center H-complex, and (3) nonlinear and nonmonotonic relation between the NH stretching vibration frequency and the energy of complex formation.     

Solvatochromism of Heteroaromatic Compounds: VII. Bifurcate Hydrogen Bond in Solvatochromic Complexes of 2-(1,2,2-Tritricyanovinyl)pyrrole

IR and UV spectrosocopy and quantum chemistry were used to reveal a bifurcate (three-center) hydrogen bond in the complexes of 2-(1,2,2-tricyanovinyl)pyrrole with hydrogen-bond acceptors. In the gas phase and aprotic inert solvents this compound exists predominantly as the sp conformer stabilized by intra- molecular hydrogen bond involving an orthogonal system of the nitrile group and the NH hydrogen. The formation of the three-center hydrogen bond with an aprotic protophilic solvent shifts the conformational equilibrium to the ap conformer. As the strength of the intermolecular hydrogen bond increases in the series nitromethane < acetonitrile < dioxane, the fraction of the ap conformer increases and becomes prevailing already in the moderately protophilic THF. Solvatochromism of the long-wave absorption band in the elec- tronic spectra of the sp and ap conformers was studied in detail.     

Solvatochromism of Heteroaromatic Compounds: XXV. Effect of Bifurcate Hydrogen Bond with a Weak Intramolecular Component on the IR,NMR, and UV Spectra of 2,6-Dibromo-4-nitrophenol

Dissolution of 2,6-dibromo-4-nitrophenol in aprotic protophilic solvents forms a three-center solvation H-complex with a sharply weakened intramolecular hydrogen bond. This weakening is associated with a deformation of the bond angle of the hydroxy group. It is only on interaction with weak π-bases that the intramolecular component of the bifurcate hydrogen bond appreciably affects the spectral position of the OH stretching vibration band; this results in a nonlinear dependence between OH and the Kamlet-Taft sol-vatochromic parameter.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 1, 2005, pp. 111–122.Original Russian Text Copyright © 2005 by Fedorov, Krivoruchka, Shulunova, Sherstyannikova, Trofimova, Vokin, Turchaninov.     

Solvatochromism of Heteroaromatic Compounds: XX. 4(5)-Nitroimidazole

4(5)-Nitroimidazole in solution is stabilized as the 5-nitro isomer due to formation of hydrogen bond with an aprotic protophilic solvent. Amphiprotic medium favors displacement of the tautomeric equilibrium toward the 4-nitro isomer via formation of a solvate complex where 4-nitroimidazole acts as hydrogen bond acceptor. The observed specific solvatochromic effect in the UV spectrum of 4-nitroimidazole and related heterocyclic nitro compounds is determined by the electronic configuration of the excited ,^*-state.     

Solvatochromism of Heteroaromatic Compounds: XII. Solvatochromism and Tautomerism of 4-Methyl-3-nitro-1,2,4-triazol-5-one in Aprotic Solvents

The long-wave absorption band in the UV spectrum of 4-methyl-3-nitro-1,2,4-triazol-5-one is highly sensitive to specific solvation by hydrogen bonding with a protophilic solvent. The UV and IR spectra suggest that the compound mainly exists in the form of the N¹H tautomer. The qualitative and quantitative relationships characterizing the solvent effect on the spectral characteristics of the major tautomer were elucidated.     

Solvatochromism of Heteroaromatic Compounds: X. 2-Phenylpyrrolide Anion

2-Phenylpyrrolide anion was obtained in high-polarity media containing MeONa as an ionizing agent. The bathochromic shift of the long-wave absorption band in going from the neutral to deprotonated form is explained by the difference in the molecular orbital characteristics of the parent molecule and the anion, as well as the by change in the equilibrium conformation on deprotonation. According to ab initio calculations, the conformational rearrangement contributes partly to the observed shift; the greatest contribution is from the destabilization of the highest occupied molecular orbital.     

Solvatochromism of Heteroaromatic Compounds: VIII. 2-(Tricyanovinyl)-5-phenylpyrrole

Rotational isomerism of 2-(tricyanovinyl)-5-phenylpyrrole and formation of complexes with a three-centered (bifurcational) hydrogen bond were studied by UV spectroscopy and quantum-chemical calculations. In the gas phase and in weakly and moderately protophilic media these compounds have mainly the syn-periplanar form stabilized by the intramolecular hydrogen bond involving the orthogonal system of the nitrile group and the NH hydrogen atom. No intermolecular H complex is formed in such solvents. In tetrahydrofuran, cyclohexanone, pyridine, and some other media a complex conformational equilibrium is observed. Interaction with aliphatic alcohols, amides, dimethyl sulfoxide, and triethylamine results in stabilization of the H complex of the anti-periplanar conformer.     

Solvatochromism of Heteroaromatic Compounds: XI. 1-Ethyl-2-formylbenzimidazole

Two regression dependences of the energy of the intramolecular charge-transfer transition in 1-ethyl-2-formylbenzimidazole on the polarity and polarizability of the medium have been established; one relates to the syn-periplanar conformer and the other, to the anti-periplanar conformer. The different solvatochromism of the two molecular forms is associated with the different sensitivity of low-energy electronic transitions of these conformers to nonspecific solvation.     

Solvatochromism of Heteroaromatic Compounds: XXIII. Reversible Specific Solvatochromic Effect in the IR Spectra of 2-Nitrophenol and 2,4,6-Trinitrophenol

2-Nitrophenol and 2,4,6-trinitrophenol form with protophilic solvents complexes with a bifurcate (three-center) hydrogen bond. Their O-H stretching vibration frequencies nonlinearly and unsteadily vary with the H-bond acceptor ability of the medium, which is a spectroscopic evidence for three-center H-complex formation.     

Solvatochromism of Heteroaromatic Compounds: XXI. Ion Pairs of 4-Nitropyrazolide Anion

The solvatochromism of the long-wave UV absorption band of the contact ion pairs of the 4-nitropyrazolide anion with alkali metal cations in aprotic protophilic solvents with 24 was studied and quantitatively described using the Kamlet-Taft empirical solvent parameters. Of two possible types of tight ion pairs differing in the murtual arrangement of the counterions, the solvent stabilizes the pair in which the cation is located in the plane of the anion in the vicinity of its nitrogen atoms. Among the factors affecting the quantitative characterisitcs of the solvatochromism of such ion pairs, the major factors are the polarity/polarizability of the solvent and the capability of its molecules for coordination with cations. The peripheral specific solvation of the cation in an ion pair stabilizes its Franck-Condon excited state relative to the ground electronic state. In the quantitative respect, this effect is similar to that characteristic of solvation H complexes.     

Solvatochromism of Heteroaromatic Compounds: XIII. Methyl(aroyloxymethyl)fluorosilanes and (Aroyloxymethyl)trifluorosilanes

The UV spectra of heptane solutions of methyl(aroyloxymethyl)fluorosilanes and (aroyloxymethyl)trifluorosilanes of the general formula 4-RC₆H₄COOCH₂Si(Me)_{3 - 4n} F _n (n = 1-3; R = H, F, Cl, Me, MeO, O2N) were studied. The intramolecular coordination bond Oarr;Si causes a bathochromic shift of the second -* transition, because the energy gap between the ground electronic and Franck-Condon excited states decreases owing to additional stabilization of the latter. The spectral shifts correspond to stabilization of the five-coordinate state of the silicon atom in (aroyloxymethyl)trifluorosilanes by 5-6 kcal mol^{- 1}.     

Solvatochromism of Heteroaromatic Compounds: XIV. 5-Amino-1-methyl-4-nitropyrazole and Its Analogs

The solvatochromism of H complexes of 5-amino-1-methyl-4-nitropyrazole and 2-nitroaniline derivatives in aprotic protophilic media was described on a quantitative level with the aid of Kamlet-Taft empirical parameters. Specific solvation affects only one of the two long-wave bands, namely that corresponding to an electronic transition involving orbital electron density transfer from the H-bound nitrogen atom. When such transfer does not occur, which is typical of the second transition, specific solvatochromic effect is either weak or absent.     

Solvatochromism of Heteroaromatic Compounds: XXVI. Solvent Effect on the Solvatochromic Parameters of IR Bands of <Emphasis Type="Italic">N</Emphasis>-Methylanilines and Related Hydrogen Bond Donors

Formation of a hydrogen bond between molecules of a proton donor (phenol, pyrrole, N-methylanilines) and a solvent decreases the sensitivity of the XH stretching frequency to the polarity/polarizability of solvents. A change in the bond configuration in the amine moiety of N-methylaniline and related compounds upon formation of a solvation H complex is manifested in that the absolute terms of the solvatochromic equations for inert and protophilic media are different. The spectroscopic effect from the geometric reorganization of molecules is determined by their structure and the capability to act as hydrogen bond donors. Multicentered hydrogen bond with π bases affects the geometry of the amine fragment of N-substituted anilines to a lesser extent than does two-centered H bond with onium bases.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 642–649.Original Russian Text Copyright © 2005 by Vokin, Oznobikhina, Shulunova, Ustinov, Bozhenkov, Levkovskaya, Turchaninov.For communication XXV, see [1].     

Solvatochromism of Heteroaromatic Compounds: XVIII. Reversible Effect of the Medium on the UV spectra of 2-(2-Benzoyl-1-phenylethenyl)-5-phenylpyrrole

Theoretical (B3LYP/6-31G^*) and experimental (NMR, UV, and IR spectroscopy) data on the electronic and steric structure of 2-(2-benzoyl-1-phenylethenyl)-5-phenylpyrrole have been analyzed in the context of the hypothesis of the zwitter ionic nature of its ground state. The molecule involves a strong NH···O bond, and its ground state can be described as a hybrid of the neutral and zwitter ionic canonical forms; this conclusion was confirmed by the observation of a reversible medium effect on the electronic absorption spectrum of the substrate.     

Solvatochromism of Heteroaromatic Compounds: XVII. Effect of Aprotic Inert Solvents on the Structure of 2-(2,2-Dicyanovinyl-1-methylthio)-5-methylpyrrole

The effect of aprotic inert media on the conformational structure of 2-(2,2-dicyanovinyl-1-methylthio)-5-methylpyrrole was studied by UV, NMR, and IR spectroscopy. Chloroform and less polar solvents stabilize only one of the four conformers. In more polar media, there is a dynamic equilibrium between all the possible conformers of the title compound. The state of the equilibrium depends both on the solvent and on the temperature.     

Röntgenstrukturanalyse von N-((E)-2-Methyl-2-butenyl)-N-(4-methylphenylsulfonyl)-N′-(4-nitrophenyl)schwefeldiamid

X-Ray Structure Analysis of N-((E)-2-Methyl-2-butenyl)-N-(4-methylphenylsulfonyl)-N′-(4-nitrophenyl)sulfurdiamide The title compound crystallizes in the monoclinic space group P2₁/n with a = 16.893(3), b = 14.285(2), c = 18.422(4), β = 114.765(5)°, V = 4037 ų, Z = 8. The formal S? N single bonds of the diaminosulfane moiety are shortened and differ in length (1.700 and 1.644 Å). The bonds of the N? S? N group to the p-nitrophenyl and tosyl rest are also a bit shorter than single bonds. The hybridization of the N atoms of the N? S? N moiety is sp² with a tendency in the direction of sp³. Analogously to open chained sulfur diimides with respect to the N? S? N moiety an E/Z configuration can be derived. In the crystal structure the molecules are connected to one-dimensional polymers via hydrogen bridges between the nitrogen of the secondary amino group as a donor and an oxygen of the nitro group as an acceptor.     

Synthesis of 2- [ (4-Hydroxylcarbomylphenyl) -methylamino ] - N- ( 2- aminophenyl ) acetamide

Early studies revealed that the hybrid polar/apolar compound N, N′-hexamethylene bisacetaamide (HMBA) was a very effective inducer of differentiation in a transformed cell lines. [1] The use of this polar/apolar compound to induce murine erythroleukemia cells (MELC) to undergo erythoid differentiation with suppression of oncogenicity has proved a useful model to study inducer-mediated differentiation of transformed cell. [2] To search more effective inducers, we utilized the computer to design a new target compound. Herein, we reported the synthesis of title compound.     

N-(2,3-Dihydroxy-4-iodo-2,3-dimethylbutyl)trifluoroacetamide: Hydrogen Bonds in Crystal and Solution

Russian Journal of General Chemistry - The structure of N-(2,3-dihydroxy-4-iodo-2,3-dimethylbutyl)trifluoroacetamide and its dimers has been studied in the crystal, solution, and gas phase by means...