The α-Effect in Nucleophilic Substitution Reactions of Y-Substituted-Phenyl Diphenylphosphinates with HOO− and OH− 


Vol. 34,  No. 8, pp. 2251-2255, Aug.  2013
10.5012/bkcs.2013.34.8.2251


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  Abstract

Second-order rate constants (kHOO−) for the nucleophilic substitution reactions of Y-substituted-phenyl diphenylphosphinates (4a-4i) with HOO− in H2O have been measured spectrophotometrically. The α-nucleophile HOO− is 10-70 times more reactive than the reference nucleophile OH− although the former is ca. 4 pKa units less basic than the latter, indicating the α-effect is operative. The Brønsted-type plot for the reactions of 4a-4i with HOO– is linear with βlg = –0.51, a typical βlg value for reactions which were reported to proceed through a concerted mechanism. The Yukawa-Tsuno plot is also linear with ρ = 1.40 and r = 0.47, indicating that a negative charge develops partially on the O atom of the leaving group, which can be delocalized to the substituent Y through resonance interactions. Thus, the reactions have been proposed to proceed through a concerted mechanism. The magnitude of the α-effect (i.e., the kHOO−/kHO− ratio) decreases linearly as the leaving-group basicity increases. It has been concluded that solvation effect is not solely responsible for the α- effect found in this study but the transition-state stabilization through an intramolecular H-bonding interaction is also responsible for the α-effect.

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  Cite this article

[IEEE Style]

H. Hong, A. R. Bae, I. Um, "The α-Effect in Nucleophilic Substitution Reactions of Y-Substituted-Phenyl Diphenylphosphinates with HOO− and OH−," Bulletin of the Korean Chemical Society, vol. 34, no. 8, pp. 2251-2255, 2013. DOI: 10.5012/bkcs.2013.34.8.2251.

[ACM Style]

Hyo-Jeong Hong, Ae Ri Bae, and Ik-Hwan Um. 2013. The α-Effect in Nucleophilic Substitution Reactions of Y-Substituted-Phenyl Diphenylphosphinates with HOO− and OH−. Bulletin of the Korean Chemical Society, 34, 8, (2013), 2251-2255. DOI: 10.5012/bkcs.2013.34.8.2251.

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ISSN(Print) 0253-2964
ISSN(Online) 1229-5949