摘要:

AbstractAn interface for a Canberra Model 7880 fast multiscaler and an Extranuclear quadrupole controller with an IBM PC is described. With the interface and using only a few keystrokes one can choose to take either a mass spectrum or a time‐of‐flight spectrum of a given mass. The limitations and the minor modifications of the original hardware are also discus

ISSN:0009-4536    

DOI:10.1002/jccs.198800011

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractTricarbonyl(4‐alkoxyl‐1‐alkylcyclohexadienylium)iron complexes (I) react with metal‐cation enolate nucleophiles to give in most cases a mixture of products (II) and (III), resulting from attack at the C‐1 and C‐5 termini of the dienylium ring. Factors that control the regioselectivity of nucleophilic addition, including the steric and electronic effects of the 4‐alkoxyl and 1‐alkyl substituents, the degree of association between the enolate nucleophiles and their counterions, and the polarity of the solvents, we

ISSN:0009-4536    

DOI:10.1002/jccs.198800012

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe kinetics of the Finkelstein reactions of benzyl halides and halide ions in dry acetone was studied by using the GC and HPLC methods. The method of conductivity is used to measure the degree of dissociation of alkali halide in acetone. The dissociation of the salt and the common‐ion effect were used to correct the halide ion concentration. Letkxx′‐ andKxx′‐ represent the corrected second‐order rate constant and equilibrium constant for the PhCH2X‐X′‐ reaction, respectively, then at 25°kxx‐−= 1.83x×10−3M−1s−1,KII‐=4.48×104,kBrcl‐=0.377M−1s−1,KBrcl‐=874; andkBr‐=7.88M−1s−1,KIBr‐=19.2. The entropy of activation is always negative which implies that the activated complex is more solvated than the reactants. There is a good correlation between the enthalpy of activation and the C‐X bond energy. The enthalpy of activation is much smaller than the corresponding C‐X bond energy which implies that both the bond formation and the bond dissociation are taking place simultaneously in the transition state. A modified Taft equation is used to correlate the Finkelstein reactions of alkyl halides (RCH2X). However, the benzyl halides can not be fit by the correlation equation due to the strong electrical polar effects. Discussion of the Finkelstein reactions of organic halides in terms of rate constants, equilibrium constants, solvent effects

ISSN:0009-4536    

DOI:10.1002/jccs.198800013

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractAn atomic absorption method has been developed for the determination of selenium in synthetic mixtures of geological samples. Thiourea andn‐butylamine are added as a matrix modifier for the precise and accurate determinatio

ISSN:0009-4536    

DOI:10.1002/jccs.198800014

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY