Alcohols, acidity rotational barriers

Tautomerism has been investigated in 3,5-dimethyl-2-(2 -pyridyl)pyrrole and 3,5-di-/< /t-butyl-2-(2 -pyridyl)pyrroles in the gas phase, in their alcohol complexes, and as dimers <2004PCP3938>. The compounds exist preferentially in the normal ry -conformation, which in the dimethyl compound is energetically favored over the /f-conformation by 4.3 kcal moP with a rotational barrier of 11.3 kcal mol , and are more stable than their tautomers in the gas phase. Tautomerism is observed in pyrrole-2,5-diacetic acid and its diethyl ester with the pyrrole form being favored for the free acid and the pyrrolidinediylidene tautomer for the diester <2003NJC1353>. 

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