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Phenylnitrenium ions were generated from phenyl azides in the presence of trifluoroacetic acid (TFA) and/or trifluoromethanesulphonic acid (TFSA). Unsubstituted phenylnitrenium ions and those with an electron-withdrawing group such as NO2 or CN undergo aromatic N-substitution, whereas those with an electron-donating group such as Me, OMe, CH2Ph, or Ph undergo C-substitution, hydrogen abstraction, and tar formation. The special character of TFA and TFSA as compared with other acids is discussed.
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Takeuchi et al. (1986) studied this question.
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