摘要:

A novel spectroscopic method for the measurement of small relative changes of the optical absorption coefficient or thermal diffusivity is demonstrated, based on a sharp signal phase variation in PPE experiments, under well defined circumstances.

ISSN:0038-7010    

DOI:10.1080/00387019208017855

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A thin copper foil placed diagonally in a cylindrical copper hollow cathode undergoes fast erosion caused by cathode sputtering. Changes in the foil shape are related to current distribution along the hollow cathode axis. The experimental results aid in understanding the increase in spectral lines intensities emitted from conical bottom hollow cathode lamps.

ISSN:0038-7010    

DOI:10.1080/00387019208017856

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The 60 MHz1H NMR spectra of 3-ethyl-3-phenylpyrrolidine-2,5-dione,1, were studied in CDCl3at 28° using the achiral lanthanide shift reagent (LSR) tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III), Eu(FOD)32, for spectral simplification, and the chiral LSR, tris[3-heptafluoropropylhydroxymethylene)-(+)-camphorato]-europium(III), Eu(HFC)33, to induce enantiomeric shift differences (δδδ) for several nuclei. A non-racemic sample of1was treated with3to determine the sense of magnetic nonequivalence of selected nuclei. Significant δδδ is seen for the signals of the methyl and arylorthoprotons. Modest δδδ can also be seen for the NH signal and for one of the H-4 protons, although LSR-induced broadening for the two latter signals is severe. The (-) enantiomer appeared to exhibit an upfield sense of magnetic nonequivalence (3:1molar ratio ca. 0.15—0.35) for the methyl signal but a downfield sense for Hortho(3:1ratio ca. 0.6).

ISSN:0038-7010    

DOI:10.1080/00387019208017857

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Natural abundance17O NMR data for 14 substituted methyl N-arylcarbamates obtained in acetonitrile solution at 75°C are reported. The17O NMR chemical shifts of hinderedorthoN-arylcarbamates are shielded relative to unhindered ones; a quantitative relationship is observed between the carbonyl17O NMR chemical shifts and molecular mechanics (MM2) predicted torsion angles. The carbonyl17O NMR chemical shifts ofmetaandparasubstituted N-arylcarbamates are correlated with Hammett sigma constants.

ISSN:0038-7010    

DOI:10.1080/00387019208017858

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Carbon-13 NMR chemical shifts of a series of (E)- and (Z)-N-ethyl-N-methylamides [RC(O)NEtMe, R=H, Me, Et,i-Pr,t-Bu, CF3, ClCH2, Cl2CH, Cl3C, BrCH2, Br2CH, Br3C and ICH2] are reported. The α-carbon and carbonyl carbon chemical shifts are correlated with the empirical α-substituent effect and Charton's electrical parameter ([sgrave]I), respectively. The N-alkyl carbon resonances were attributed mainly to the γ- and δ-effects of R.

ISSN:0038-7010    

DOI:10.1080/00387019208017859

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Two effects in optogalvanic detector—hollow cathode discharge are reported. They appear at light irradiation of the detector and interfere with its properties. First effect, connected with Penning process in Ar-Cd plasma, is used for identification of negative plasma resistance. The other effect is a light induced potential on the cathode.

ISSN:0038-7010    

DOI:10.1080/00387019208017860

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Raman and infrared spectra of Boc-(D-aIle-L-Ile)3-OMe (ILEU-6) and its N-deuterated derivative have been measured. Conformationally sensitive amide vibrations have been identified and compared with the observed and calculated frequencies of Pro-Leu-Gly-NH2which has a type II β-turn structure. The observed frequencies of ILEU-6 have also been compared with the normal mode calculations of a standard model type II β-turn structure and a good agreement has been found in these comparisons. The additional frequencies observed for this particular structure are assigned to the residues that are not involved in the β-turn.

ISSN:0038-7010    

DOI:10.1080/00387019208017861

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The molecular structure of tribromoethanol has been studied by Ab Initio theoretical calculations. The IR spectrum has been recorded in the range 4000—200 cm−1. Whereas, the Raman spectrum has been determined by means of a SPEX 1403 spectrometer using the 5145Å exciting line of a Spectra—Physics 164 Ar ion laser. Depolarization ratios were also measured. The fundamental vibrations of CBr3CH2OH as well as some overtones, combinations and difference bands were assigned.

ISSN:0038-7010    

DOI:10.1080/00387019208017862

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A glow discharge system for atomic emission spectrometry is evaluated for physical and analytical characteristics. Lead (as the nitrate) is the model element used for these studies. The sputtering characteristics of several electrode designs are studied with the best system tried resulting in total sample vaporization in less than 1 s. Discharge currents up to 200 mA at a discharge voltage of 1200 V and a pressure of 2 torr are found to give the best results. The detection limit for lead is 0.9 ng and the linear dynamic range of response is greater than 2 orders of magnitude. Sodium chloride at a 100-fold excess amount causes a 50% decrease in the signal level.

ISSN:0038-7010    

DOI:10.1080/00387019208017863

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effects of substituents on the13C chemical shifts of the various carbons of aliphatic 1,2-bis(amidinohydrazones) have been systematically studied using previously published experimental data as the basis. Mathematical formulae have been constructed that describe the effects of various structural features of the molecules on the chemical shifts of the carbons and that also make possible an accurate prediction of the spectra of compounds belonging to this class. It is also shown that the effects of side chains on the chemical shifts of the two carbons of the glyoxal moiety are strictly additive. A mathematical model has been constructed that makes possible a very accurate prediction of the chemical shift of each one of the glyoxal carbons of symmetrical as well as unsymmetrical bis(amidinohydrazones). In the case of ethylmethylglyoxal bis(amidinohydrazone) free base dissolved in dimethyl sulfoxide, the theory predicts that the glyoxal carbons resonate at 157.45 ppm (the one connected to the ethyl group) and 151.21 ppm, while the experimental values are 157.30 and 151.29 ppm. This has, for the first time, made possible the unambiguous individual assignment of the resonances of the glyoxal carbons of unsymmetrical dialkylglyoxal bis(amidinohydrazones). The results also indicate that in all such compounds so far studied, that one of the glyoxal carbons that bears the longer alkyl side chain resonates more downfield than does the other one. This result is in total agreement with conclusions derived from relaxation time measurements.

ISSN:0038-7010    

DOI:10.1080/00387019208017864

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor