B Hydroxyarenium Ions

For sulphuric acid. 344,345) position of absorption maxima of unsubstituted 4-hydroxy- and 4-methoxybenzenium ions was the subject of discussions. No reliable experimental measurements are yet available. 

A similar character to the spectra of the above ions is observed with the complexes of tautomeric phenols with AIX3 

The long-wave absorption maximum of the 2-hydroxybenzenium ion seems to be located near 360 nm. Introduction of the 4-HO group results in its hypsochromic shift by about 50 nm, and that of the 6-HO group, in a bathochromic shift by about 30 nm. The effect of 1-, 3-, 4-, 5- and 6-CH3 groups is about -t-5, -1-15, —10, -f-25 and -I-20 nm, respectively (Table 34). 

From these data one could expect the long-wave absorption maximum of the unsubstituted ion to be located near 330-335 nm (cf. rather than at 420 nm as found in Molecular orbital calculations in different approximations yield values for the long-wave absorption maximum of the unsubstituted benzenium ion varying from 375-400 nm 92. i6A29) 

In addition to the data in Tables 33 and 34 the absorption maxima for the 2,4,6-trimethoxybenzenium ion in 63.5% HCIO are located at 347 and 247 nm (Igs is equal to 4.09 and 4.31) spectra of other ions containing alkoxy groups 

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