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

Bulletin of the Korean chemical society

Hyo-Jeong Hong¹  Ik-Hwan Um¹  Ae Ri Bae¹ 

关键词: The -effect;    Ground state;    Transition state;    Solvation effect;    H-bonding interaction;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

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.

【 授权许可】

Unknown