USING INCOMING GROUP C-11 C-14 KINETIC ISOTOPE EFFECTS TO MODEL THE TRANSITION-STATES FOR THE S(N)2 REACTIONS BETWEEN PARASUBSTITUTED BENZYL CHLORIDES AND LABELED CYANIDE ION/

A large incoming group C-11/C-14 kinetic isotope effect of 1.0104 +/- 0.0023 has been measured for the S(N)2 reaction between benzyl chlorid e and labeled cyanide ion in 20% aqueous DMSO at 30.00 degrees C. Thes e large incoming group kinetic isotope effects have also been measured for the S(N)2 reactions of other para-substituted benzyl chlorides wi th cyanide ion. A combination of the incoming group C-11/C-14 and chlo rine (Hill J. W.; Fry, A., J. Am. Chem. Sec. 1962, 84, 2763) leaving g roup kinetic isotope effects have been used to model the S(N)2 transit ion states for these reactions. Adding a more electron-withdrawing par a substituent to the substrate does not affect the stronger N=C- - -C- alpha reacting bond significantly but shortens the weaker C-alpha- - - Cl reacting bond markedly.