摘要:

The electronic absorption spectra of nicotinamide were measured in seventeen aprotic solvents. The solvatochromic method is used to unravel solvent polarity and hydrogen bonding effects on π − π* transition. Solvent effects are rationalized in terms of the solvatochromic parameters: π*, δ, α, and β.

ISSN:0038-7010    

DOI:10.1080/00387019008054437

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The O‒H…π interaction between proton donor systems phenol, substituted phenols, benzyl alcohol and cyclohexanol and proton acceptor systems benzene, toluene, m- and p-xylenes, naphthalene and anthracene have been studied by infrared spectroscopy. It is found that the strength of the O‒H…π hydrogen bonding decreases in the following order: phenol > benzyl alcohol > cyclohexanol, and phenol > cresol> 2,6-dimethyl phenol > 2,4,6-tri-tret&utyl phenol. The strength of the proton acceptors, on the other hand, decreases in the fol lowing order: xylene > toluene > benzene > chlorobenzene, and for polyaromatic bases the trend is benzene > naphthalene > anthracene.

ISSN:0038-7010    

DOI:10.1080/00387019008054438

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Benzene-induced shifts (BIS) in the1H NMR spectra of nine chromeno-compounds have been studied. It provides a simple non-destructive technique for distinguishing linear isomers of chromenoflavones from their angular counterparts. BIS also assists in the assignment of chromene proton signals in chromeno-compounds.

ISSN:0038-7010    

DOI:10.1080/00387019008054439

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The influence of the aprotic Solvents on the1H NMR spectra of the N-H proton has been studied. The chemical shift shows quite good correlation with the solvatochromic parameters, π*, β, and α, while a fair correlation with the Gutmann donor and acceptor numbers were obtained.

ISSN:0038-7010    

DOI:10.1080/00387019008054440

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

At frequencies above one megahertz, the behaviour of electrolytic solutions changes from an ionic conductor to a lossy dielectric. High frequency conductance measurements of aqueous electrolytes (Na2SO4and KCl) have been made by continuous wave and pulse admittance methods, in cells with immersed, shiny Pt electrodes to study this transition. Peak conductance frequencies as a function of concentration did not conform to the classical circuit representation of a resistance and capacitance. Measured phase angles indicate that relatively concentrated electrolytes (0.001 − 1 M) exhibit inductance due to electromagnetic and perhaps mass (inertial) effects. Modelling was possible with a constant value of the inductance, L, and capacitance, C, using a simple RLC equivalent circuit. Ion and solvent perturbations in high frequency electrical fields first are discussed in terms of a damped harmonic oscillator model, whose macroscopic response is self-consistent and equivalent mathematically to RLC network. However, it is improbable that mass effects are sufficiently large to explain the majority of the inductance, which arises primarily from the transmission of energy through the solution. Obviously, the skin effects found in electrolytes will be distinct from those for metallic conductors.

ISSN:0038-7010    

DOI:10.1080/00387019008054441

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The 60 MHz1H NMR spectra of racemic (+)-cis-4,5-dihydro-4-methyl-5-phenyl-2-oxazolamine,1, have been studied at 28° in CDC13, solution with the achiral lanthanide shift reagent (LSR), tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium(III), 2, and the chiral reagent tris[3−(heptafluoropropylhydroxymethy1ene)-d-camphor-ato]europium(III), 3. Additional NMR studies were performed at 400 MHz in CDC1, solution at 24° using the chiral solvating agents (CSA), (E)-(-)-2,2,2-trifluoro-1- (9-anthryl) ethanol,4, and (R) - (+) -α-methoxy- α-(trifluoromethy1)phenylacetic acid,5. Substantial enantiomeric shift differences, for the CH3, signal of1using3or5, and for the ortho aryl protons using4, which should make possible direct optical purity determinations of1. Accurate 400 MHz data f o r chemical shifts and vicinal coupling constants of, of racemiccis-1are presented, and compared with values for (optically active) (-)-trans-1; some dfferences are seen compared to previously reported data. solution. The LSR and CSA results are compared and Some additional data were obtained in C6D6discussed.

ISSN:0038-7010    

DOI:10.1080/00387019008054442

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In a preceding work(1)we have studied the UV-Visible spectrum of pterocarpin, a natural product which is known, with many of its derivatives, for its antifungal properties.(2–6)The molecule of pterocarpin contains the benzodioxole moiety (figure I) whose presence could be a factor favourable to such properties. Furthermore, some of the benzodioxole derivatives are known as popular drug of abuse (ecstasy).(7–10)Among our studies on the benzodioxole derivatives substituted in para to one of the oxygen atoms, we present in that paper the results of our UV spectroscopic investigations. This work concerns molecules with substitutents weakly interacting with the π system (i.e. substituents whose type is-CH2X), since the spectra of these molecules display a basic phenomenon which has never been observed.

ISSN:0038-7010    

DOI:10.1080/00387019008054443

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The absorption, excitation and fluorescence spectra of fluorescein in ethyl acetate and acetone were obtained. It was verified that the neutral lactonic form of fluorescein is present in dilute solutions of those organic solvents. However, in concentrated solutions it was observed a shift of the dissociation equilibrium to form the neutral zwitterionic form of the dye in both electronic ground and excited states.

ISSN:0038-7010    

DOI:10.1080/00387019008054444

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The electron-vibrational (vibronic) bands of light absorption by mixed valence molecular crystals containing clusters of transition metal ions in different states of oxidation as the structural units of lattice are considered. The absorption band shape calculation in different phase states is performed in the semiclassical limit for crystals consisting of trielectronic clusters of transition metals of the type of d1-d2. The band shape differs from the Gaussian and closely depends on the double-exchange and Heisenberg-type exchange parameters and on the temperature dependence of the average dipole moment playing the role of the order parameter.

ISSN:0038-7010    

DOI:10.1080/00387019008054445

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We made the superconductor of Bi2Sr2CaCu2Oγby the solid state reaction. According to the results of measurement by infrared spectrophotometer with the varying of wave number from 4000 to 400 cm−1. We discovered three infrared absorption peaks at room temperature, i.e., peak A1at 500–550 cm−1, peak A2at 800–840 cm−1and peak A3at 1370–1420 cm−1. We find that peak A1is due to impure phase, peak A2is related with the crystal structure and peak A3is caused by the vibration of the atom layers of calcium.

ISSN:0038-7010    

DOI:10.1080/00387019008054446

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor