Abstract
New methods are described for the preparation of substituted pyrylium halides. Pyrylium iodides have a different colour and an additional charge-transfer absorption band in the crystalline state and in dichloromethane solution as compared with the corresponding perchlorates. The position of the CT band is intermediate between that of tropylium and pyridinium halides. The effect of phenyl groups on the CT band of pyrylium iodides, which is markedly different from the effect on the x-band from the absorption spectrum or on the polarographic half-wave potentials is tentatively explained by the symmetry properties of the lowest empty molecular orbital, thus accounting for the correlation with the y-band from the absorption spectrum.
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