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A Mechanistic Study on Addition Reactions of Alicyclic Amines to 3-Butyn-2-one

Title
A Mechanistic Study on Addition Reactions of Alicyclic Amines to 3-Butyn-2-one
Authors
Um I.-H.Lee J.-S.Yuk S.-M.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
1998
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 19, no. 7, pp. 776 - 779
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants have been measured spectrophotometrically for the addition reaction of a series of alicyclic amines to 3-butyn-2-one to yield their respective enamines at 25.0°C. The reactivity of the amines increases with increasing the basicity of the amines. However, the Brönsted-type plot obtained exhibits a downward curvature as the basicity of the amines increases, i.e. βnuc decreases from 0.3 for low basic amines (pKa < 9) and to 0.1 for highly basic amines (pKa > 9). Such a curvature in the Brönsted-type plot is clearly indicative of a change in the reaction mechanism or transition state structure. From the corresponding reactions run in D2O, the magnitude of kinetic isotope effect (KIE) has been calculated to be about 0.8 for highly basic amines and 1.21 for weakly basic amines. The difference in the magnitude of KIE also supports a change in the reaction mechanism or transition state structure upon changing the basicity of the amines. Furthermore, the small KIE clearly suggests that H+ transfer is not involved in the rate-determining step, i.e. the addition reaction is considered to proceed via a stepwise mechanism in which the attack of the amines to the acetylene is the rate-determining step. The curvature in the Brönsted-type plot has been attributed to a change in the degree of bond formation between the amine and the acetylene.
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자연과학대학 > 화학·나노과학전공 > Journal papers
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