Synthesis, tautomeric forms, specific intermolecular interactions, and lipophilicity of methylated 6-hydroxypyridazine-3-carboxylic acid and its 4,5-dihydro analogs

► H-tautomers of pyridazine and 4,5-dihydropyridazine carboxylic acids. ► Methylation of pyridazine and 4,5-dihydropyridazine carboxylic acids. ► Lipophilicity of the methylated products and their intermolecular interactions. ► Reverse lactam-lactim tautomers in pyridazine and its 4,5-dihydro analog.