Stable carbocations and onium ions from

Stable carbocations and onium ions from polycondensed aromatic and heteroaromatic compounds as models for biological electrophiles and DNA-transalkylating agents... 

Two chapters in this volume describe the generation of carbocations and the characterization of their structure and reactivity in strikingly different milieu. The study of the reactions in water of persistent carbocations generated from aromatic and heteroaromatic compounds has long provided useful models for the reactions of DNA with reactive electrophiles. The chapter by Laali and Borosky on the formation of stable carbocations and onium ions in water describes correlations between structure-reactivity relationships, obtained from wholly chemical studies on these carbocations, and the carcinogenic potency of these carbocations. The landmark studies to characterize reactive carbocations under stable superacidic conditions led to the award of the 1994 Nobel Prize in Chemistry to George Olah. The chapter by Reddy and Prakash describes the creative extension of this earlier work to the study of extremely unstable carbodications under conditions where they show long lifetimes. The chapter provides a lucid description of modern experimental methods to characterize these unusual reactive intermediates and of ab initio calculations to model the results of experimental work. 

Preparation of Carbocations, Onium Ions, and Their Salts. SbFs is a preferred medium for the preparation of carbocations and onium ions. In fact, the first observation of stable carbocations was achieved in this medium. - By dissolving /-butyl fluoride in an excess of SbFs, the /-butyl cation was obtained (eq 26). Subsequently, many alkyl cations have been obtained in SbFs (either neat or diluted with SO2, SO2CIF, or SO2F2). The 2-norbomyl cation, one of the most controversial ions in the history of physical organic chemistry, was prepared from exo-2-fluoronorbomane in SbFs/S02 (or SO2CIF) solution (eq 27). Bridgehead cations such as 1-adamantyl, 1-trishomobarrelyl, and 1-trishomobullvalyl cations have also been similarly prepared with the use of SbFs. ... 

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