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Effect of modification of the electrophilic center on the α effect

Title
Effect of modification of the electrophilic center on the α effect
Authors
Um I.-H.Lee J.-Y.Bae S.-Y.Buncel E.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2005
Journal Title
Canadian Journal of Chemistry
ISSN
0008-4042JCR Link
Citation
vol. 83, no. 9, pp. 1365 - 1371
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
We report on a nucleophilic study of esters R-C(=X)-Y-Ar in which the electrophilic center has been modified by replacing O by S in the leaving group or carbonyl center: 4-nitrophenyl acetate (1), S-4-nitrophenyl thioacetate (2), 4-nitrophenyl benzoate (3), and O-4-nitrophenyl thionobenzoate (4). The studies include O - and S - nucleophiles as well as α nucleophiles in H 2O at 25.0 ± 0.1°C. The sulfur nucleophile (4-chlorothiophenoxide, 4-ClPhS -) exhibits significant enhanced reactivity for the reactions with thiol and thione esters 2 and 4 compared with their oxygen analogues 1 and 3. On the contrary, the common nucleophile OH - is much less reactive towards 2 and 4 compared with 1 and 3. The effect of changing both the electrophilic center and the nucleofugic center on the reactivity of the other oxygen nucleophiles is not so significant: 4-chlorophenoxide (4-ClPhO -) is four to six times more reactive in the reactions with thiol and thione esters 2 and 4 compared with their oxygen analogues 1 and 3. The α effects exhibited by butan-2,3-dione monoximate (Ox -) and HOO - are strongly dependent on the nature of the electrophilic center of the substrates, indicating that the difference in the ground-state solvation energy cannot be fully responsible for the α effect. Our results clearly emphasize the strong dependence of the α effect on the substrate structure, notably, the nature of the electrophilic center. The impact of change in the nucleofuge (1-→2) and the electrophilic center (3-→4) on reactivity indicates that ánucleophiles will need to be "purpose built" for decontamination and nucleophilic degradation of specific biocides. © 2005 NRC Canada.
DOI
10.1139/v05-157
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자연과학대학 > 화학·나노과학전공 > Journal papers
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