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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 26, Number 4
BKCSDE 26(4)
April 20, 2005 

 
Title
Kinetics and Mechanism of the Addition of Benzylamines to β-Cyanostilbenes in Acetonitrile
Author
Hyuck Keun Oh*, In Kon Kim, Dae Dong Sung, Ikchoon Lee*
Keywords
Nucleophilic addition, β-Cyanostilbene, Cross-interaction constant, Kinetic isotope effects, Concerted mechanism
Abstract
Nucleophilic addition reactions of benzylamines (XC6H4CH2NH2) to β-cyanostilbenes (YC6H4CH=C(CN)C6H4Y’) have been studied in acetonitrile at 30.0 oC. A greater degree of N-C α bond formation (larger βX) is obtained with a stronger electron-withdrawing substituent in either α- ( δσY > 0) or β-ring ( δσY’ > 0). A stronger charge development is observed in the TS on C β ( ρY’ = 1.06 for X=Y=H) rather than on C α ( ρY = 0.62 for X=Y’=H) indicating the lag in the resonance development into the activating group (CN) on C β in the transition state. Similarly, the magnitude of ρXY’ (?0.72) is greater than ρXY (?0.66) due to a stronger interaction of the nucleophile with β-ring than α-ring. The positive sign of ρYY’ correctly reflects π bond cleavage between the two rings in the TS. Relatively large kinetic isotope effects (kH/kD ≥ 2.0) involving deuterated nucleophiles (XC6H4CH2ND2) suggest a four-membered cyclic TS in which concurrent N-C α and H(D)-C β bond formation occurs.
Page
641 - 644
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