View : 25 Download: 0

S<inf>N</inf>Ar reactions of 1-halo-2,4-dinitrobenzenes with alkali-metal ethoxides: Differential stabilization of ground state and transition state determines alkali-metal ion catalysis or inhibition

Title
S<inf>N</inf>Ar reactions of 1-halo-2,4-dinitrobenzenes with alkali-metal ethoxides: Differential stabilization of ground state and transition state determines alkali-metal ion catalysis or inhibition
Authors
Yang K.Kim M.-Y.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2015
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 36, no. 7, pp. 1812 - 1818
Keywords
Alkali-metal ion catalysis or inhibitionElectrophilicityNucleofugalityS<inf>N</inf>Ar reaction
Publisher
Korean Chemical Society
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
A kinetic study on S<inf>N</inf>Ar reactions of 1-halo-2,4-dinitrobenzenes (6a-6d) with alkali-metal ethoxides (EtOM; M = Li, Na, K and 18-crown-6-ether-complexed K) is reported. The plots of pseudo-first-order rate constant (k<inf>obsd</inf>) vs. [EtOM] curve upward or downward depending on the size of M+ ions. The reactions are catalyzed or inhibited by the M+ ions, e.g., the large K+ ion complexed by 18-crown-6-ether (18C6) acts as a catalyst while the small Li+ and Na+ ions behave as an inhibitor. Reactivity of 6a-6d toward EtOM decreases linearly as the halide ion becomes less basic regardless of the size of M+ ions, indicating that expulsion of the leaving group occurs after the rate-determining step (RDS). Thus, the reactions have been proposed to proceed through a stepwise mechanism with formation of a Meisenheimer complex being the RDS. Computational studies using B3LYP density functional theory have revealed that Mulliken charge density of the electrophilic center decreases as the halogen atom becomes less electronegative. Thus, it has been concluded that the S<inf>N</inf>Ar reactivity of 6a-6d toward EtOM is governed by electrophilicity of the reaction center but not by nucleofugality of the leaving group. A π-complexed transition-state structure has been proposed to account for the experimental and computational results. © 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
DOI
10.1002/bkcs.10344
Appears in Collections:
자연과학대학 > 화학·나노과학전공 > Journal papers
Files in This Item:
There are no files associated with this item.
Export
RIS (EndNote)
XLS (Excel)
XML


qrcode

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

BROWSE