Generation of the Parent Allyl Cation in a Superacid Cryogenic Matrix

By using cyclopropyl bromide as precursor , the allyl cation C 3 H can be generated at low temperature in an SbF 5 matrix and observed by IR spectroscopy; the experimental IR spectrum agrees well with that computed by ab initio methods. Characterization by 13 C NMR spectroscopy failed, but the 13 C NMR chemical shifts of this and other allyl cations could be predicted accurately for the first time by the GIAO/MP‐2 method.