Thio acid/azide amidation: an improved route to N-acyl sulfonamides

[STRUCTURE: SEE TEXT] A one-pot procedure for the conversion of carboxylic acids to N-acyl sulfonamides, via thio acid/azide amidation, is presented. The method is compatible with acid- and base-sensitive amino acid protection. N-Acyl sulfonamide synthesis on solid support, peptide thio acid/sulfonazide coupling, and N-alkyl amide synthesis via selective cleavage of sulfonyl from an N-alkyl-N-acyl sulfonamide are also reported.     

A theoretical study of solvent effects on molecular electronic properties

INDO parameterized molecular orbital calculations, including the solvaton model, are employed in a study of medium effects on solute eigenfunctions and eigenvalues. Some resulting molecular electronic properties are compared with available experimental data for some model compounds. In general, reasonable agreement between the two sets of results is obtained for those molecular properties such as conformational equilibria, rotational energy barriers, hydrogen bonding and tautomeric equilibria which are germane to drug-receptor interaction studies.     

A theoretical study on nitration mechanism of benzene and solvent effects

Aromatic nitration is an important and canonical example of electrophilic substitution in organic chemistry. The research on nitration mechanism is also very important for synthesis of explosives since benzene molecule is a basic unit to build up into the energetic material. Besides the electrophilic substitution mechanism, there is an electron transfer mechanism[1,2]. The nitronium ion (NO+ 2), however, is a generally accepted active nitrating agent in the aromatic nitration. Therefore, the …     

A solvent induced mechanism for conformational change

Molecular dynamics simulations have been used to investigate the dynamic behaviour of two small molecule neurotransmitter analogues in aqueous solution, leading to the elucidation of a mechanism for conformational change which is driven by the presence of the solvent molecules.     

Local solvent density augmentation around a solute in supercritical solvent bath: 1. A mechanism explanation and a new phenomenon

A recently proposed partitioned density functional (DF) approximation (Phys. Rev. E 2003, 68, 061201) and an adjustable parameter-free version of a Lagrangian theorem-based DF approximation (LTDFA: Phys. Lett. A 2003, 319, 279) are combined to propose a DF approximation for nonuniform Lennard-Jones (LJ) fluid. Predictions of the present DF approximation for local LJ solvent density inhomogeneity around a large LJ solute particle or hard core Yukawa particle are in good agreement with existing simulation data. An extensive investigation about the effect of solvent bath temperature, solvent-solute interaction range, solvent-solute interaction magnitude, and solute size on the local solvent density inhomogeneity is carried out with the present DF approximation. It is found that a plateau of solvent accumulation number as a function of solvent bath bulk density is due to a coupling between the solvent-solute interaction and solvent correlation whose mathematical expression is a convolution integral appearing in the density profile equation of the DF theory formalism. The coupling becomes stronger as the increasing of the whole solvent-solute interaction strength, solute size relative to solvent size, and the closeness to the critical density and temperature of the solvent bath. When the attractive solvent-solute interaction becomes large enough and the bulk state moves close enough to the critical temperature of the solvent bath, the maximum solvent accumulation number as a function of solvent bath bulk density appears near the solvent bath critical density; the appearance of this maximum is in contrast with a conclusion drawn by a previous investigation based on an inhomogeneous version of Ornstein-Zernike integral equation carried out only for a smaller parameter space than that in the present paper. Advantage of the DFT approach over the integral equation is discussed.     

A new theory for polymer/solvent mixtures based on hard-sphere limit

Based on hard-sphere limit of binary mixtures with different molecular size of components a theory has been developed for calculating activities of solvents in polymer/solvent mixtures. The theory considers various chain configurations for polymer molecules, varying from extended chain to the coiled chain. According to this theory the activity of solvent can be calculated from molecular weights (MWs) and densities as the only input data. The only adjustable parameter in the calculations, is the hard-sphere diameter of polymer, which provides useful criteria for the judgement on the chain configuration of polymer.The activity calculations have been performed for seven binary mixtures of polymer/solvent and compared with experimental data at various temperatures and for a varying range of MWs of polymers.The solvents in the mixtures were both of polar and nonpolar natures. The activity calculations for the same systems were performed by the well-known Flory-Huggins theory. Comparing the results of calculations with those of Flory-Huggins theory indicates that, the proposed theory is able to predict the activities of the solvent with good accuracy.The radius of gyration, excluded volume and interaction parameter for polymer chain have been calculated using the parameter obtained in the new theory. The calculated interaction parameter in the new theory, is interpreted in terms of attraction, repulsion and interchange energy of polymer and solvent in the mixture.     

Substituent and solvent effects on electronic spectra of some substituted phenoxyacetic acids

The effects of substituents and solvents have been studied through the absorption spectra of nearly 19 para- and ortho-substituted phenoxyacetic acids in the range of 200-400 nm. The effects of substituent on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.     

A new synthesis of naphthyridinones and quinolinones: palladium-catalyzed amidation of o-carbonyl-substituted aryl halides

[reaction: see text] An alternative to the Friedlander condensation for the synthesis of naphthyridinones and quinolinones has been discovered. Palladium-catalyzed amidation of halo aromatics substituted in the ortho position by a carbonyl functional group or its equivalent with primary or secondary amides leads to the formation of substituted naphthyridinones and quinolinones.     

Theoretical investigation of the electronic spectra of aromatic nitrosooxides with allowance for solvent effects

Density functional theory methods correctly describe some properties of nitrosooxides. Electronic spectral data have been calculated for seven para-substituted aromatic nitrosooxides in different solvents using the UB3LYP/6-311+G(d,p) approximation. The calculated positions of maxima in UV spectra correlate with experimental data with high coefficient. Equations are suggested for predicting the positions of absorption maxima for the para-R-C₆H₄-NOO under study.     

The elusive mechanism of olefin metathesis promoted by (NHC)Ru-based catalysts: a trade between steric, electronic, and solvent effects

The reaction mechanism operative in olefin metathesis has been and still is a challenging area of research. Here we contribute to the discussion showing that the actual mechanism is a balance of the title effects. In particular, we show that the electronic and solvent effects evidenced by experimental studies can be easily counterbalanced by steric effects.     

Semiempirical calculations of the electronic spectra of organometallic compounds: Estimation of solvent and counterion effects

The electronic spectra of the [Ru(NH₃)₅pz]²⁺, [Ru(NH₃)₅pz]³⁺, and [Ru(CN)₅pz]³⁻ complexes are calculated by the CI INDO method. The effect of solvation on the spectra is considered in a point charge approximation and in terms of the parametric model of a charged sphere enveloping the metal fragment. Interrelation of these approaches is discussed. Data on the molecular electrostatic potentials created by the complexes are presented to substantiate the models. St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 603–618, July–August, 1996. Translated by I. Izvekova     

Quantum-chemical calculations of solvent effects on the electronic structure and reactivity of molecules

Journal of Structural Chemistry -     

A new method for estimating excited state dipole moments of molecules from the solvent effect on their electronic spectra

Some comments are made on the paper entitled “Excited state dipole moments of some monosubstituted benzenes from the solvent effect on electronic absorption spectra” by Prabhumirashi et al. (Spectrochim. Acta 39A, 663,1983) and a new method, which has been tested on some molecules and found satisfactory, is suggested for estimating the excited state dipole moment of molecules from the solvent effect on their electronic spectra.     

Electronic structures of carbazole and indole and the solvent effects on the electronic spectra

The results of the experimental studies on the solvent effects upon the fluorescence and the absorption spectra of carbazole and indole are described, which makes it possible to estimate the difference of the electronic structures in the fluorescence state from those in the ground state.The electronic structures of the molecules are studied theoretically on the basis of the experimental results.

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Zusammenfassung Die Beeinflussung der Absorptions- bzw. Fluoreszenzspektren von Carbazol und Indol durch Lösungsmitteleffekte wird untersucht. Aus den Ergebnissen werden Rückschlüsse auf die Elektronenstrukturen der Grund- und Fluoreszenzzustände gezogen. Eine auf den experimentellen Resultaten basierende theoretische Behandlung der Elektronenstrukturen schließt sich an.

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Résumé Nous avons étudié les effects de solvant sur les spectres d'émission et d'absorption du carbazol et de l'indole. Les résultats permettent des conclusions sur la différence entre les structures électroniques des états excité et fondamental. Des calculs sur ces structures sont faits à l'aide des données expérimentales.

     

A new sensitive and specific test for cobalt

Summary The p-nitrophenylhydrazone of 3-isonitrosopentane-2-one gives in ammoniacal solution a red coloration with cobalt, which provides a sensitive and specific test. Cyanide as well as a high concentration of ammonium salts prevent the test. Palladium, silver, nickel, copper and most common cations and anions do not interfere.

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Zusammenfassung Dasp-Nitrophenylhydrazon von 3-Isonitrosopentan-2-on gibt in ammoniakalischer Lösung mit Kobalt eine Rotfärbung, die dessen empfindlichen und spezifischen Nachweis ermöglicht. Cyanid sowohl wie eine hohe Ammoniumsalzkonzentration verhindern die Probe. Palladium, Silber, Nickel, Kupfer und die meisten der gewöhnlichen Kationen und Anionen verursachen keine Störung.

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Résumé Lap-nitrophenylhydrazone de l'isonitroso-3 pentanone-2 donne en solution ammoniacale une coloration rouge avec le cobalt que l'on utilise comme essai sensible et spécifique. Les cyanures, ainsi que de fortes concentrations en sels de l'ammonium, gênent l'essai. Le palladium, l'argent, le nickel, le cuivre et les cations et anions les plus fréquents n'interfèrent pas.