A New Type of Nonbenzenoid Aromatic Carbocation : 1, 6-Methano[10]AnnulenylCation.

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The structure-reactivity relatioship of a new type of nonbenzenoid aromatic carbocation with a positive charge on an unsaturated carbon atom, 1, 6-methano[10]annulen-2-yl cation, was investigated by theoretical and experimental methods.a. A comparison of experimental results in solvolysis with theoretical calculations by semiempirical MO methods with respect to the structure-stability relationship of carbocations with a positive charge on an unsaturated canbon atom indicated that the carbocation 30 kcal/mol more stable than phenyl cation can be generated in the S_N1 solvolysis of the corresponding triflate precursors.b. Incontrast to planar 1-naphthyl cation, 1, 6-methano[10]annulen-2-yl cation is highly stabilized by the delocalization of the positive charge on C-2 atom into 10 pi electron system because of its nonplanar structure and the contribution of a limiting allene structure.c. 1, 6-Methano[10]annulen-2-ylcation was generated in gas phase from the corresponding annulenyl bromide derivative.d. The solvolysis of the annulenyl triflate in trifluoroethanol (TFE) gave complex mixtures containing some products by triflate substitution with TFE solvent.e. An experiment of quantitative dideuterio substitution of the 2, 7-dibromoannulene derivative indicated a possibility of the generation of the annulenyl cation in the beta-decay decomposition of the corresponding 2, 7-ditritioannulene derivative in gas phase and solution phase.