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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 8
BKCSDE 32(8)
August 20, 2011 

 
Title
Transition State Variation in the Anilinolysis of O-Aryl Phenyl Phosphonochloridothioates in Acetonitrile
Author
Keshab Kumar Adhikary, Bilkis Jahan Lumbiny, Shuchismita Dey, Hai Whang Lee *
Keywords
Phosphoryl transfer reaction, Deuterium kinetic isotope effect, Cross-interaction constant, O-Aryl phenyl phosphonochloridothioates, Transition state variation
Abstract
The nucleophilic substitution reactions of Y-O-aryl phenyl phosphonochloridothioates with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are kinetically investigated in acetonitrile at 55.0 oC. The deuterium kinetic isotope effects (DKIEs) invariably increase from an extremely large secondary inverse (kH/kD = 0.439; min) to a primary normal (kH/kD = 1.34; max) as both substituents of nucleophile (X) and substrate (Y) change from electron-donating to electron-withdrawing. These results are opposite to the DKIEs on Y-O-aryl methyl phosphonochloridothioates, and can be rationalized by the gradual transition state (TS) variation from backside to frontside attack. The trigonal bipyramidal pentacoordinate TS is proposed for a backside attack, while the hydrogen-bonded, four-center-type TS is proposed for a frontside attack. The negative values of the cross-interaction constants (ρXY(H) = −0.38 for XC6H4NH2 and ρXY(D) = −0.29 for XC6H4ND2) indicate that the reactions proceed by a concerted SN2 mechanism.
Page
2628 - 2632
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