Aromatic protonation—part 2 : 1H NMR parameters of the anthracenium ions of some 9-alkyl-, 9-alkyl-α-chloro-, 9,10-dialkyl-anthracenes and 1-chloroanthracene. study on the sit

Abstract

Seventeen 9-alkylanthracenes ( 1–17) and 1-chloroanthracene have been protonated with FSO 3H in SO 2CIF as cosolvent at −78°. For all substrates C(10) protonation was observed, but with some substrates in addition C(9) protonation, if that would lead to relief of steric strain between the substituent at C(9) and the substituent(s) at C(1) [and C(8)]. The C(9) protonated ions exist in the preferred conformation IIa. The ions resulting on ipso-protonation of the 9,10-dialkyl-anthracenes have a similar type of conformation. Based both on this preferred conformation and the peri-chloro effects of the anthracenium ions, it is concluded that these ions are best represented by the equilibirum IIa ⇌ IIb.