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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 26, Number 6
BKCSDE 26(6)
June 20, 2005 

Kinetics and Mechanism of the Addition of Benzylamines to α-Cyano-β-phenylacrylamides in Acetonitrile
Hyuck Keun Oh*, Myoung Hwa Ku, Hai Whang Lee
Nucleophilic addition reaction, Single-step process, Cross-interaction constant, Kinetic isotope effect, Four-center cyclic transition state
Nucleophilic addition reactions of benzylamines (BA; XC6H4CH2NH2) to α-cyano-β-phenylacrylamides (CPA; YC6H4CH=C(CN)CONH2) have been investigated in acetonitrile at 25.0 oC. The rate is first order with respect to BA and CPA and no base catalysis is observed. The addition of BA to CPA occurs in a single step in which the addition of BA to Cβ of CPA and proton transfer from BA to Cα of CPA take place concurrently with a four-membered cyclic transition state structure. The magnitude of the Hammett (ρX) and Bronsted (βX) coefficients are rather small suggesting an early tansition state (TS). The sign and magnitude of the crossinteraction constant, ρXY (= -0.26), is comparable to those found in the normal bond formation processes in the SN2 and addition reactions. The normal kinetic isotope effect (kH/kD > 1.0) and relatively low ΔH≠ and large negative ΔS≠ values are also consistent with the mechanism proposed.
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