Conformation and tautomerism of the cimetidine molecule: a theoretical study |
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Authors: | Gra?yna Karpińska Jan Cz Dobrowolski Aleksander P Mazurek |
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Institution: | a National Institute of Public health, 30/34 Che?mska Street, 00-725 Warsaw, Poland b Industrial Chemistry Research Institute, 8 Rydygiera Street, 01-973 Warsaw, Poland |
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Abstract: | The cimetidine molecule conformation and tautomer stability was studied at the ab initio HF/6-31G** level and for single point energies at the MP2/6-31G** level. The most stable N3-H cimetidine tautomer was found to be more stable than the most stable N1-H tautomer by ca. 3.7 and 5.0 kcal/mol, at the HF/6-31G** and MP2/6-31G**//HF/6-31G** level, respectively. At the HF/6-31G** level, the most stable N3-H and 1-H forms are stabilized by the intramolecular N3′-H?N1 hydrogen bond and N1-H?N4′, respectively. However, when the correlation effects are included at the MP2/6-31G**//HF/6-31G** level, the most stable N3-H and N1-H tautomers appeared to be folded forms without hydrogen bonds. |
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Keywords: | Ab initio Cimetidine Conformation Intramolecular hydrogen bond Tautomerism |
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