Bulletin of the Korean Chemical Society | |
Kinetic Study on Nucleophilic Substitution Reactions of O‐Phenyl O‐Y‐substituted‐Phenyl Thionocarbonates with 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene in Acetonitrile | |
Hwan Um1  Ik‐2  Kyoung‐3  | |
[1] Department of Chemical and Molecular Engineering Hanyang University Ansan Gyeonggi‐Department of Chemistry Ewha Womans University Seoul 03760 Korea;do 15588 Korea | |
关键词: O‐; Phenyl O‐; Y‐; substituted‐; phenyl thionocarbonates; 1,8‐; Diazabicyclo[5.4.0]undec‐; 7‐; ene; Steric hindrance; Forced concerted mechanism; Brø; nsted‐; type plot; | |
DOI : 10.1002/bkcs.11242 | |
学科分类:化学(综合) | |
来源: Korean Chemical Society | |
【 摘 要 】
Secondâorder rate constants (kN) for nucleophilic substitution reactions of Oâphenyl OâYâsubstitutedâphenyl thionocarbonates (4aâ4k) with 1,8âdiazabicyclo[5.4.0]undecâ7âene (DBU) in MeCN at 25.0â±â0.1°C are reported. The reactivity of 4aâ4k decreases as basicity of the leaving group increases except Oâ2,4âdinitrophenyl Oâphenyl thionocarbonate (4a), which is less reactive than Oâ3,4âdinitrophenyl Oâphenyl thionocarbonate (4b) although the former possesses 2 pKa units less basic nucleofuge than the latter. The Brønstedâtype plot for the reactions of 4bâ4k is linear with βlgâ=ââ0.50, a typical βlg value for reactions reported to proceed through a concerted mechanism. The Hammett plot correlated with ÏYâ constants for the reactions of 4bâ4k results in a better linear correlation than that correlated with ÏYo constants. Besides, the YukawaâTsuno plot exhibits an excellent linear correlation with ÏYâ=â2.12, râ=â0.68 and R2â=â0.990, indicating that a negative charge develops partially on the O atom of the leaving group in the rateâdetermining step (RDS). Thus, the reactions have been concluded to proceed through a forced concerted mechanism. Effects of steric hindrance on reactivity and reaction mechanism are also discussed in detail.
【 授权许可】
Unknown
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