MECHANISM OF THE REACTION OF PICRYL IODIDE WITH 4-[4-(DIMETHYLAMINO)STYRYL]PYRIDINE

We have used semiempirical calculations (PM3, MNDOd) to show that the parabolic dependence of the rate constants (kobs, s–1) on the picryl iodide (PicI) concentration in the reaction of quaternization of 4-[4-(dimethylamino)styryl]pyridine (DASP) in acetonitrile is due to formation of an inactive _1,3 adduct from DASP and PicI. Formation of the sigma1,1 adduct is the rate-limiting step of the SNAr substitution.