The absorption spectra of the pyridine in various solvents were measured from 400 mμ to 210 mμ.Electronic absorption bands were observed in the regions 335300 mμ (I), 295260 mμ (II), and 270230 mμ (III).
The most weak band (I) has sub-peaks in the n-hexane solution.Increasing polarity of solvents, this band is diffused and intensified, but the band position is nearly unchanged. Then, this Band (I) will be identified as a singlet-triplet π-electronic transition band.
The next band (II) has nearly equal absorption curves in n-hexane, dioxane and ether solutions, but is absent in alcohol and water solutions.Another band (III) has a diffuse maximum in n-hexane, dioxane and ether solutions but shows more intense sub-parks in alcohol and water solutions. From these behaviors, the band (II) and the band (III) were respectively identified as a n-electronic transition band and a lowest π-electronic transition band.These solvent effects in alcohol and water solutions will be attributed to hydrogen bonding between the pyridine N atom and the OH-group of solvents.
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