Blue Shift of the Visible Diiodine Transition Upon Halogen Bonding to Pyridines

10 Blue Shift of the Visible Diiodine Transition Upon Halogen Bonding to Pyridines 

Among the uses of the correlations that have been established between spectroscopic and thermodynamic scales of basicity, the calculation of new thermodynamic values appears of primary importance in the context of the quantitative measurement of Lewis basicity. In fact, it is generally easier and faster to measure a spectroscopic shift than an equilibrium constant. This experiment illustrates the calculation of p Tbi, values for three pyridines. 

3-iodopyridine, 3-(trifluoromethyl)pyridine and 4-(tTifluoromethyl)pyridine, from the correlation between the diiodine basicity and the blue shift of the visible diiodine transition, established in Chapter 5 for 3- and 4-substituted pyridines (Equation 7.46)  

The standard error of the estimate, s, is very close to the experimental uncertainty on 

P Tbi2 (about 0.05). Thus, the diiodine basicity of any 3- and 4-substituted pyridine can 

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