Acta Crystallographica Section C

Crystal Structure Communications

Volume 64, Part 11 (November 2008)

organic compounds

sf3092 scheme

Acta Cryst. (2008). C64, o590-o594 [ doi:10.1107/S010827010803206X ]

Keto-enol tautomerism in crystals of 3-[hydroxy(phenyl)methyl]-2,5,7-trimethyl-2,3-dihydropyrido[3,2-e][1,2]thiazin-4-one 1,1-dioxide and 3-(1-hydroxyethylidene)-2,5,7-trimethyl-2,3-dihydropyrido[3,2-e][1,2]thiazin-4-one 1,1-dioxide

Z. Karczmarzyk

Abstract: In the crystal structures of the title compounds, C₁₇H₁₆N₂O₄S, (I), and C₁₂H₁₄N₂O₄S, (II), the co-existence of both possible keto/enol (4-keto and 4-hydroxy) tautomers, with visible predominance of the 4-keto form, is observed. The tautomeric equilibrium is stabilized by strong intramolecular O-HO hydrogen bonding. The ¹³C NMR spectra recorded for (I) and (II), and theoretical calculations at the RHF SCF ab initio 6-31G** level, show the same tautomeric equilibrium in solution and the gaseous phase. The partially saturated thiazine rings in the pyrido[3,2-e][1,2]thiazine rings systems of (I) and (II) adopt a diplanar conformation. The molecular packing in (I) is influenced by weak intermolecular C-HO hydrogen bonding and C-H [pi] interactions. In the crystal structure of (II), the molecules are linked by a combination of O-HO hydrogen bonding and C-H [pi] and [pi] - [pi] interactions.

Formula: C₁₇H₁₆N₂O₄S and C₁₂H₁₄N₂O₄S


	Structure factor file (CIF format) (194.2 kbytes) [ doi:10.1107/S010827010803206X/sf3092Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (148.9 kbytes) [ doi:10.1107/S010827010803206X/sf3092IIsup3.hkl ] Contains datablock II

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