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1718234 
Journal Article 
NO2+ nitration mechanism of aromatic compounds: Electrophilic vs charge-transfer process 
Tanaka, M; Muro, E; Ando, H; Xu, Q; Fujiwara, M; Souma, Y; Yamaguchi, Y 
2000 
Yes 
Journal of Organic Chemistry
ISSN: 0022-3263
EISSN: 1520-6904 
65 
10 
2972-2978 
WOS:000087262500018 
The nitration of methylnaphthalenes with NO2BF4 and NOBF4 was examined in order to shed light on the controversial aromatic nitration mechanism, electrophilic vs charge-transfer process. The NO2+ nitration of 1,8-dimethylnaphthalene showed a drastic regioselectivity change depending on the reaction temperature, where ortho-regioselectivity at -78 degrees C and para-regioselectivity at 0 degrees C were considered to reflect the electrophilic and the direct or alter native charge-transfer process, respectively, because the NO+ nitration through the same reaction intermediates as in the NO2+ nitration via a charge-transfer process resulted in para-regioselectivity regardless of the reaction temperature. The NO2+ nitration of redox potential methylnaphthalenes higher than 1,8-dimethylnaphthalene gave a similar ortho-regioselectivity enhancement to 1,8-dimethylnaphthalene at lower temperature, thus reflecting the electrophilic process. On the other hand, the NO2+ nitration of redox potential methylnaphthalenes lower than 1,8-dimethylnaphthalene showed para-regioselectivity similar to the NO+ nitration, indicating the direct or alternative charge-transfer process. In the presence of strong acids where the direct charge-transfer process will be suppressed by protonation, the ortho-regioselectivity enhancement was observed in the NO2+ nitration of 1,8-dimethylnaphthalene, suggesting that the direct charge-transfer process could be the main process to show para-regioselectivity. These experimental results imply that the NO2+ nitration proceeds via not only electrophilic but also direct charge-transfer processes, which has been considered to be unlikely because of the high energy demanding process of a bond coordination change between NO2+ and NO2. Theoretical studies at the MP2/6-31G(d) level predicted ortho- and para-regioselectivity for the NQ(2)(+) nitration via electrophilic and charge-transfer processes, respectively, and the preference of the direct charge-transfer process over the alternative one, which support the experimental conclusion.