| Abstract
| - The photoinduced proton transfer reaction taking place in2-(2‘,4‘-dinitrobenzyl)pyridine (α-DNBP) and insome of its derivatives is characterized by IR, visible, and NMRspectroscopy. The enamine “NH” structureof the blue phototautomer is confirmed by the analysis of the IRspectra of α-DNBP and its deuteratedanalogue. 2D NOESY 1H NMR data indicate that thistautomer is predominantly in the cisconfiguration.In the 2-(2‘,4‘-dinitrobenzyl)phenanthroline derivative, thestabilization of the phototautomer is sufficient tomake it thermally accessible. A quantitative analysis of theresulting thermochromism indicates that in toluenesolutions the ground state energy of the “NH” form is lowered to2.9 kcal mol-1 above thethermodynamicallystable “CH” tautomer compared to more than 8 kcalmol-1 in the parent α-DNBPcompound.
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