2402-74-6Relevant academic research and scientific papers
Doubly Destabilized Carbocations. Strong Aryl Delocalization and the Attenuation of Rate Decelerating Effects of CF3 and CN Groups
Allen, Anette D.,Kanagasabapathy, V. M.,Tidwell, Thomas T.
, p. 3470 - 3474 (2007/10/02)
Solvolysis rates of ArC(CF3)2OTs in CF3CO2H give an excellent correlation log k = -10.7?+-8.69, and a point for the p-Me2N compound derived from the rate of the p-nitrobenzoate also fits this correlation, giving a span of 1E19 in reactivity.Limiting values of ρ+ of -10 to -12 for generation of benzylic cations in the gas phase and solution have been reached.Rate ratios k(ArCH(OTs)CF3)/k(ArC(CF3)2OTs) increase from 2.4 to 54 with decreasing aryl donor power; these k(H)/k(CF3) ratios are much less than typical values of 1E6 in more stabilized systems.Displacement of the p-MeO group occurs in solvolysis of p-MeOC6H4C(CF3)2OTs (9) in EtOH and CD3OH.Trifluoroacetolysis of ArC(OTs)(CF3)CN (Ar = p-Tol (13) and Ph) gives ρ+ = -12.1, and for 13 in different solvents the reactivity is greater than p-TolCH(OTs)CF3 by factors of 8.6 to 175.This is the first observation of k(CN)/k(H) ratios greater than 1.0.All these results, plus the rather modest dependence of the rates on solvent polarity (m = 0.76 for 9 and 0.66 for 13), are interpreted in terms of carbocationic transition states and intermediates in which the charge is largely delocalized onto the aryl group.
