58765-11-0Relevant articles and documents
Isoflavone biosynthesis in Onobrychis viciifolia: Formononetin and texasin as precursors of afrormosin
Al-Ani, Hakim A.M.,Dewick, Paul M.
, p. 2337 - 2339 (1980)
4,2′,4′-Trihydroxychalcone- [carbonyl-14C], formononetin- [Me-14C] and texasin- [Me-14C] were all good precursors of afrormosin (7-hydroxy-6,4′-dimethoxyisoflavone) in Onobrychis viciifolia seedlings, and a biosynthetic pathway involving these intermediates is proposed. 2′,4′-Dihydroxy-4-methoxychalcone- [carbonyl-14C] and daidzein-[carbonyl-14C] were poor precursors. Incorporations into formononetin were also recorded.
A kinetic study on nucleophilic displacement reactions of aryl benzenesulfonates with potassium ethoxide: Role of K+ ion and reaction mechanism deduced from analyses of LFERs and activation parameters
Um, Ik-Hwan,Kang, Ji-Sun,Shin, Young-Hee,Buncel, Erwin
supporting information, p. 490 - 497 (2013/03/13)
Pseudofirst-order rate constants (kobsd) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates 4a-f and Y-substituted phenyl benzenesulfonates 5a-k with EtOK in anhydrous ethanol. Dissection of k obsd into kEtO- and kEtOK (i.e., the second-order rate constants for the reactions with the dissociated EtO - and ion-paired EtOK, respectively) shows that the ion-paired EtOK is more reactive than the dissociated EtO-, indicating that K + ion catalyzes the reaction. The catalytic effect exerted by K + ion (e.g., the kEtOK/kEtO- ratio) decreases linearly as the substituent X in the benzenesulfonyl moiety changes from an electron-donating group (EDG) to an electron-withdrawing group (EWG), but it is independent of the electronic nature of the substituent Y in the leaving group. The reactions have been concluded to proceed through a concerted mechanism from analyses of the kinetic data through linear free energy relationships (e.g., the Bronsted-type, Hammett, and Yukawa-Tsuno plots). K+ ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a cyclic transition state (TS) rather than by increasing the nucleofugality of the leaving group. Activation parameters (e.g., ΔH? and ΔS?) determined from the reactions performed at five different temperatures further support the proposed mechanism and TS structures.
Combined dual substituent constant and activation parameter analysis assigns a concerted mechanism to alkaline ethanolysis at phosphorus of Y-substituted phenyl diphenylphosphinates
Um, Ik-Hwan,Park, Jee Eun,Shin, Young-Hee
, p. 3539 - 3543 (2008/09/20)
Second-order rate constants have been measured for reactions of Y-substituted phenyl diphenylphosphinates (1a-h) with EtO-K + in anhydrous ethanol. A linear Bronsted-type plot is obtained with βLg = -0.54, a typical βLg value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with σo and σ- constants are linear but exhibit many scattered points, while the corresponding Yukawa-Tsuno plot results in excellent linear correlation with r = 0.41. The r value of 0.41 indicates that the leaving group departs at the rate-determining step (RDS) whether the reactions proceed through either a concerted or a stepwise mechanism. However, a stepwise mechanism in which departure of the leaving group occurs at the RDS is excluded since the incoming EtO- ion is much more basic and a poorer leaving group than the leaving aryloxide. The ΔH? values determined in the current reactions are strongly dependent on the nature of the substituent Y, while the ΔS ? values remain constant on changing the substituent Y in the leaving group, i.e., from Y = H to Y = 4-NO2 and Y = 3,4-(NO 2)2. These ΔH? and ΔS ? trends also support a concerted mechanism. The Royal Society of Chemistry.
