Benzenium Ions with Heteroatomic Substituents

Vibrational spectra of arenium ions with heteroatomic substituents are very scarce. The protonation of hexamethylcyclohexa-2,5-dienone 71) and -2,4-dienone forming the complex (77) HCl - 2 AlClj in CHjClj shifts the stretching vibration band of the carbon-oxygen bond from 1615 cm (C=0)to 1510 cm (see also The band of the OH group at 3450cm and the before mentioned data are in good agreement with those of the PMR, i.e. the complex is a salt of the 4-hydroxy-1,1,2,3,5,6-hexamethylbenzenium ion (57 a) 

The IR spectra of 1,3,5-triaminobenzene, its monohydrochloride and trihydrochloride proved the assumption that the monohydrochloride has the structure of the chloride of the 2,4,6-triaminobenzenium ions The N—H stretching bands of the amino groups (doublet near 3300cm- ) are similar to those of free amine (3380 and 3200 cm- ) and sharply differing from that of the NHj group of the trihydrochloride which is shifted to low-frequency (to 2500 cm- ). 

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