Structure of Arenium Ions According to Physical Data

III Structure of Arenium Ions According to Physical Data 

The most reliable information on the structure of species of a new type is provided by X-ray analysis. It has so far been little applied to arenium ions. One of the few examples is the determination of the structural parameters of the tetrachloroaluminate of the heptamethylbenzenium ion . The anion of this salt is a nearly t ular tetrahedron with the Al—Cl bond equal to 2.12 A. Five sp -hybridized carbon atoms of the cation are lying in the same plane while the sp -hybridi2 d atom C, is deflected from it by 0.07 A (the angle between the planes Cj, C4, Cg and Cj, Ci, Cg is 5.4°). The mean values of the bond lengths (in A) are given in the following diagramme  

The nonplanar character of the cyclohexadienyl framework has also been noted for 2,4,6-triaminobenzenium ions (29) the angle between the planes Q C , Q and Cj, C, Cg amounts to about 15° 

At present the principal method of studying arenium ions in solutions is NMR. Interesting evidence is also derived from the analysis of vibrational and electronic spectra. The data on the structure of arenium ions obtained using these methods, as well as the spectral charactoistics of the ions, are now discussed. 

NMR spectroscopy allows one to obtain information on arenium ions generated in solutions, but also to follow their transformations. Of particular importance is the NMR spectroscopy for studying d enerate rearrangements of arenium ions. This 

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Ill Structure of Arenium Ions According to Physical Data Table 7. PMR Data of Methyl-substituted 1-Naphthalenium Ions... 

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