Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Robert V. Nauman

Abstract

The spectroscopic characteristics of neutral, protonated and deprotonated triphenylformazans were investigated by means of visible absorption and $\sp1$H NMR spectroscopies. Studies of the effect of solvents and substituents on the absorption spectra of the neutral and ionic formazans were conducted. CNDO/S calculations for a series of formazans were performed to assign the electronic transitions observed in the absorption spectra of triphenylformazan. The formazan system was found to be highly delocalized and not tautomeric as had been reported. The visible transition of the U (trans-syn) form of triphenylformazan was found to arise from orbitals localized on the formazan system. The near UV adsorption of triphenylformazan has significant charge transfer character. The spectroscopic trends displayed by neutral and ionic triphenylformazans were found to be similar to those of the $\beta$-diketones. The ionic forms of triphenylformazan derivatives were not photochromic. The anionic forms of the formazans were found to exist in equilibrium mixtures of U and S (cis-syn) isomers that absorb at different wavelengths in the visible region. The equilibrium is affected by the nature of the solvent and by the presence of substituents on the carbon phenyl ring. The cationic forms of the derivatives were found to exist almost exclusively in the U geometry. The site of protonation is believed to be one of the nitrogen atoms which has phenyl substituents.

Pages

262

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