20269-55-0Relevant articles and documents
Diastereoselective specificity for the hydrolysis of dipeptide esters in aqueous media
Ueoka, Ryuichi,Goto, Kouichi,Tanoue, Osamu,Miki, Atsushi,Yoshimitsu, Shinya,Imamura, Chikara,Ihara, Yasuji,Murakami, Yukito
, p. 73 - 74 (1999)
The diastereoselectivity for the hydrolysis of p-methoxycarbonylphenyl N-(benzyloxycarbonyl)-D(L)-phenylalanyl-L-leucinate in aqueous solution was inverted by changing concentrations of the substrates or the reaction temperature. The monomer-aggregate transition operated on the LL-substrate, which was suggested by the spectroscopic measurements, seems to be responsible for such behavior.
Heterolysis and homolysis energies for some carbon-oxygen bonds
Arnett, Edward M.,Amarnath, Kalyani,Harvey, Noel G.,Venimadhavan, Sampath
, p. 7346 - 7353 (2007/10/02)
Methods described previously for obtaining heterolysis (ΔHhet) and homolysis (ΔHhomo) enthalpies for bonds that can be cleaved to produce resonance-stabilized carbenium ions, anions, and radicals are extended to the study of carbon-oxygen bonds through the reactions of resonance-stabilized carbenium ions with substituted phenoxide ions. Titration calorimetry was used to obtain the heat of heterolysis, and the second-harmonic ac voltammetry (SHACV) method was used to obtain reversible oxidation potentials for the anions. In several cases, the electrode reactions were so fast that reversible potentials were obtained only with the greatest difficulty. Nonetheless, there is remarkably good agreement between these oxidation potentials for phenoxide ions obtained by electrochemical methods in sulfolane solution and those reported by others using entirely different techniques in different media. Such agreement provides unprecedented evidence for the soundness of the various methods used to study redox potentials of organic ions and radicals. As before, a wide variety of correlations was tested between ΔHhet and ΔHhomo. These two properties showed little correlation with each other, but ΔHhet gave good correlations between many properties for which neutral species are converted into ions or vice versa, such as redox potentials of both types of ions, the pKas of the anions, or the free energies of electron transfer. In contrast to the earlier study of cleavage to carbanions and carbenium ions, the present ΔHhet values are predicted well by a general equation that employs the pKR+ of the carbenium ion (without modification) and the pKa of the phenol. The improvement is consistent with the fact that the cleavage of carbon-oxygen bonds of the triarylcarbinols used to establish the pKR+ stability scale is a more appropriate model for the heterolysis of carbon-oxygen bonds in sulfolane at 25°C than it is for the cleavage of carbon-carbon bonds under the same conditions.
Effects of neutral and anionic substituents on the carbonyl stretching bands of substituted methylbenzoates
Vassileva, P. J.,Binev, I. G.,Juchnovski, I. N.
, p. 709 - 712 (2007/10/02)
Effects of neutral and anionic substituents on frequencies (νCO) and integrated intensities (ACO) of the carbonyl stretching bands of substituted methylbenzoates (solvent dimethyl sulphoxide) have been studied in relation to Hammett's equation: satisfactory correlations have been found between νCO and δ+ constants, as well as by using the dual-parameter equations to Yukawa, Tsuno and Taft; ACO have been found to increase in cases of strong electron-releasing substituents.It has been found that constants of anionic substituents, determined on the basis of nitrile i.r. frequencies and intensities, reflect satisfactorily the effects of these sobstituents on νCO and ACO of methylbenzoates.
