338741-97-2Relevant academic research and scientific papers
Electronic properties of the nitrone substituent. Stabilization of benzylic carbocations
Creary, Xavier,Hartandi, Kresna
, p. 97 - 102 (2007/10/03)
The nitrone substituent CH=N(O) t-Bu is electron-withdrawing with a Taft σI value of 0.20. It also retards the solvolysis rate of a cumyl chloride when placed in the meta-position (σ = 0.20). However, CH=N(O) t-Bu becomes weakly cation stabilizing when placed in the para-position of a cumyl cation (σ+ = -0.04). This weak cation stabilization is a result of a conjugative interaction which delocalizes charge and offsets the inductive effect of the nitrone. When the nitrone is placed in the para-position, but then twisted out of conjugation with the aromatic ring by incorporation of flanking 3,5-dimethyl groups, it again retards solvolysis rates. Computational studies (B3LYP/6-31G*) show that the nitrone substituent stabilizes a para-substituted benzyl cation relative to the meta-substituted analog by a conjugative interaction. However, the calculated stabilization greatly overestimates the cation stabilization seen in solvolytic reactions. Copyright
