Indazoles, acidity basicity

Photophysical experiments and theoretical calculations have been used to determine the tautomeric equilibrium between IH- and 2/f-indazoles (15a) and (15b) both in the ground (So) and in the excited state (S,) <94JPC10606>. The measurement of sublimation and solution enthalpies in water at 25°C, basicities in the excited state of 1-methylindazole (pAa = 1.61) and 2-methylindazole (pA a = 3.00), and MP2//6-31G //6-31G calculations of the difference in energy between their conjugated acids in the ground state allows the complete thermodynamic cycle to be established. Indazole in the excited state is 3.0 pA a units more acid (pA a = 1108) and 1.8 pK units more basic... 

Indazole, = 1-25, is less basic than pyrazole but a stronger N-H acid, pKa = 13.86 [121]. The tautomerism of indazole is a special case inasmuch as the 2//-indazole possesses an o-... 

Some nitrogen containing compounds were identified in the neutral fractions. There were five-membered nitrogen containing ring compounds, including indole, isoxazole, indazole, and carbazoles which do not show basic properties and consequently do not react with 1 M hydrochloric acid in the basic extraction step. A number of phthalate esters were also present in different fractions. 

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