Protonated Ethylene Carbonate: A Highly Resonance-Stabilized Cation.

Salts containing the monoprotonated ethylene carbonate species of were obtained by reacting it with the superacidic systems XF/MF5 (X=H, D; M=Sb, As). The salts in terms of [C3 H5 O3 ]+ [SbF6 ]- , [C3 H5 O3 ]+ [AsF6 ]- and [C3 H4 DO3 ]+ [AsF6 ]- were characterized by low-temperature infrared and Raman spectroscopy. In order to generate the diprotonated species of ethylene carbonate, an excess of Lewis acid was used. However, this only led to the formation of [C3 H5 O3 ]+ [Sb2 F11 ]- , which was characterized by a single-crystal X-ray structure analysis. Quantum chemical calculations on the B3LYP/aug-cc-PVTZ level of theory were carried out for the [C3 H5 O3 ]+ cation and the results were compared with the experimental data. A Natural Bond Orbital (NBO) analysis revealed sp2 hybridization of each atom belonging to the CO3 moiety, thus containing a remarkably delocalized 6π-electron system. The delocalization is confirmed by a 13 C NMR-spectroscopic study of [C3 H5 O3 ]+ [SbF6 ]- .