Carbocations matrix isolation

Closed-shell ions are among the most important intermediates in solution chemistry, and no treatise on reactive intermediates (including the present one) would be complete without extensive sections on carbocations and carbanions, if not also on heteroanalogues of the above species. Nevertheless, closed-shell ions are conspicuously absent from matrix isolation studies, apart from a few cases where such species were coincidentally formed in discharges, or where charged species were deliberately isolated by mass spectrometry (cf. Section 6.4). The reason for... 

Misic, V., Piech, K., BaUy, T. (2013). Carbocations Generated under Stable Conditions by Ionization of Matrix-Isolated Radicals The AUyl and Benzyl Cations. J. Am. Chem. Soc., 135(23), 8625-8631. 

The variations in allyl cation geometries are sensitive to the hyperconjugative interactions of alkyl substituents. Alkylated allyl cations were experimentally characterized with H-NMR, UV, and IR spectra. Recent developments of a matrix isolation technique for generating carbocations enabled the direct observation of small allyl cations with only a few stabilizing alkyl substituents. The parent allyl cation, the smallest long-lived carbocation observed in a solid SbFs matrix, could be characterized by IR but not by NMR spectroscopy. 

Vancik, H., Matrix isolation and vibrational spectroscopy of carbocations. Pure Appl. Chem., 67, 761, 1995. 

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