Carbon-13 and Oxygen-18 Kinetic Isotope Effects on Methanolysis of p-Nitrostyrene Oxide

Article abstract of DOI:10.1021/ja00267a033

Kinetic isotope effects for the acid- and base-catalyzed methanolysis of - and <8-13C>-p-nitrostyrene oxide have been measured at 30.0 deg C.In acid 94.7percent of the reaction occurs at the benzylic carbon, while in base 83.5percent occurs at the primary carbon (C(8)).In base the isotope effects k₁₆/k₁₈ and k₁₂/k₁₃ were 1.035+/-0.013 and 1.082+/-0.012, while in acid they were 1.012+/-0.011 and 0.995+/-0.012, respectively.These data complement previously determined deuterium isotope effects for the reaction in base.They suggest a late transition state in base with considerable ring opening via an S_N2 mechanism.However, in acid, the data suggest a somewhat earlier transition state with less ring opening and weaker bonding to the nucleophile than in base.