Experimental and ab initio spectra of the persistent carbocation generatedupon adsorption of vinylanisole in acid zeolites

Upon adsorption of vinylanisole on acid zeolites, a new species visually ch aracterized by its intense purple color is generated. Recent product studie s and optical spectroscopy by Cozens et al. (J. Phys. Chem. B, 1997, 101, 6 921) had previously suggested a structure of 1,3-dianisyl-2-buten-1-ylium i on (2) for this species. Herein, we have complemented the reported spectros copic characterization of the purple species by recording its IR spectrum i n a zeolite matrix. In addition, species 2 has also been generated in solut ion and its most characteristic low-field signals in C-13-NMR measured. The oretical calculations at the Hartree-Fock and B3LYP levels have been carrie d out to predict the UV/visible, IR and C-13-NMR spectra for the two more s table stereoisomers of a species such as 2. The good match between the expe rimental and calculated spectra reinforces the structural assignment of all E-2 as the actual purple species upon incorporation of vinylanisole in aci d zeolites. The degree of accuracy of the predicted spectra has been corrob orated by performing concurrently the same calculations for two structurall y related cations such as 1,3-diphenylpropenylium and 4-methoxyphenylethyli um, whose experimental spectroscopic data have already been reported in the literature.