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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 35, Number 1
BKCSDE 35(1)
January 20, 2014 

 
Title
Kinetic Study on Nucleophilic Substitution Reactions of 4-Nitrophenyl X-Substituted- 2-Methylbenzoates with Cyclic Secondary Amines in Acetonitrile: Reaction Mechanism and Failure of Reactivity-Selectivity Principle
Author
Ji-Youn Lee, Min-Young Kim, Ik-Hwan Um*
Keywords
Aminolysis, Reaction mechanism, Hammett plot, Yukawa-Tsuno plot, Brønsted-type plot
Abstract
A kinetic study is reported on nucleophilic substitution reactions of 4-nitrophenyl X-substituted-2-methylbenzoates (5a-e) with a series of cyclic secondary amines in MeCN at 25.0 ± 0.1 oC. The Hammett plots for the aminolysis of 5a-e are nonlinear, e.g., substrates possessing an electron-donating group (EDG) in the benzoyl moiety deviate negatively from the linear line composed of substrates bearing no EDG. In contrast, the Yukawa-Tsuno plots for the same reactions exhibit excellent linear correlations with X = 0.30-0.59 and r = 0.90-1.15, indicating that the nonlinear Hammett plots are caused by stabilization of the substrates possessing an EDG through resonance interactions but are not due to a change in the rate-determining step (RDS). The Brønsted-type plots are linear with nuc = 0.66-0.82. Thus, the aminolysis of 5a-e has been suggested to proceed through a stepwise mechanism in which departure of the leaving group occurs at the RDS. The X and nuc values for the aminolysis of 5a-e increase as the reactivity of the substrates and amines increases, indicating that the reactivity-selectivity principle is not applicable to the current reactions.
Page
93 - 97
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