Study of the mutual effect of the carborane nucleus and the benzene ring by the method of ultraviolet and Raman spectroscopy

Conclusions

• 1. We obtained the UV absorption spectra of 1-phenyl-o-carborane, 3-phenyl-o-carborane, 1-phenyl-m-carborane, 1,2-diphenyl-o-carborane, 1,7-diphenyl-m-carborane, and also the cesium salt of phenyldi-carbaundecarborane (13) in the 210–340 nm region.

• 2. The integral intensity of the ∼1600 cm⁻¹ line in the Raman spectra of solutions of 1-phenyl-o-carborane, 1,2-diphenyl-o-carborane, 1-phenyl-m-carborane, and benzotrifluoride in CH₂Cl₂ was measured.

• 3. The effect of the carborane nucleus on the UV absorption band of the benzene ring in the 240–280 nm region is expressed in a slight shift of the maximum, with the retention of a distinct vibrational structure and an increase in the molar absorption coefficient up to several hundred units. In contrast, in the UV spectrum of [C₆H₅CB₉H₁₀CH]⁻Cs⁺ the intensity of the same band reaches 7700; the vibrational structure is smoothed out completely.

• 4. On the basis of the UV spectra and the intensities in the Raman spectra of the phenylcarboranes it was concluded that conjugation of the benzene ring with carborane nuclei is absent, and that conjugation with the dicarbaundecarborane (13) anion exists.