27976-53-0Relevant articles and documents
Concurrent primary and secondary deuterium kinetic isotope effects in anilinolysis of O-aryl methyl phosphonochloridothioates
Ul Hoque, Md. Ehtesham,Guha, Arun Kanti,Kim, Chan Kyung,Lee, Bon-Su,Lee, Hai Whang
supporting information; experimental part, p. 2919 - 2925 (2011/02/28)
The nucleophilic substitution reactions of Y-O-aryl methyl phosphonochloridothioates with substituted anilines (XC6H 4NH2) and deuterated anilines (XC6H 4ND2) are investigated kinetically in acetonitrile at 55.0°C. The Hammett and Bronsted plots for substituent (X) variations in the nucleophiles are biphasic concave downwards with a break region between X = H and 4-Cl. The deuterium kinetic isotope effects (DKIEs) are primary normal (kH/kD = 1.03-1.30) for stronger nucleophiles (X = 4-MeO, 4-Me and H), and extremely large secondary inverse (kH/kD = 0.367-0.567) for weaker nucleophiles (X = 4-Cl, 3-Cl and 3-NO2). The cross-interaction constants are negative (ρXY(H) = -0.95 and ρXY(D) = -1.11) for stronger nucleophiles, while positive (ρXY(H) = +0.77 and ρXY(D) = +0.21) for weaker nucleophiles. These kinetic results indicate that the mechanism changes from a concerted process involving frontside nucleophilic attack for stronger nucleophiles to a stepwise process with a rate-limiting leaving group expulsion from the intermediate involving backside attack for weaker nucleophiles. A hydrogen-bonded, four-center-type transition state (TS) is suggested for a frontside attack, while a trigonal bipyramidal pentacoordinate TS is suggested for a backside attack. The unusually small DKIEs, as small as or equal to 0.4, for weaker nucleophiles seem to be ascribed to severe steric congestion in the TS.
