Journal
JOURNAL OF MOLECULAR STRUCTURE
Volume 998, Issue 1-3, Pages 84-90Publisher
ELSEVIER
DOI: 10.1016/j.molstruc.2011.05.016
Keywords
Pyridazine-carboxylic acids; Lactam-lactim tautomers; Methylation; Lipophilicity; Crystal structure
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Effects of methylation for intermolecular interactions and lipophilicity have been studied for a series of methylated 4,5-dihydro-6-hydroxypyridazine-3-carboxylic and 6-hydroxypyridazine-3-carboxylic acids (1 and 2). In solution they exist in equilibrium of the lactam and lactim tautomers, with the reverse preferences for analogs 1 and 2, which affect the syntheses of their methylated derivatives. Carboxylic acid 2 preferably crystallizes as a hydrate, built of carboxylate anions and hydronium cations 2(-)center dot H3O+, hydrogen bonded into catemeric patterns involving both ions. In methyl 4,5-dihydro-6-oxopyridazine-3-carboxylate (4A) the molecules are NH center dot center dot center dot O hydrogen bonded into chains. In both structures 2(-)center dot H3O+ and 4A, there are relatively strong CH center dot center dot center dot O hydrogen bonds, arranging the molecules into sheets. The increased lipophilicity of the methylated derivatives has been correlated with the formation of CH center dot center dot center dot O bonds. (C) 2011 Elsevier B.V. All rights reserved.
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