title: 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.
abstract: In the crystal structures of the title compounds, C(17)H(16)N(2)O(4)S, (I), and C(12)H(14)N(2)O(4)S, (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-H...O hydrogen bonding. The (13)C 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-H...O hydrogen bonding and C-H...pi interactions. In the crystal structure of (II), the molecules are linked by a combination of O-H...O hydrogen bonding and C-H...pi and pi-pi interactions.
authors.affiliation: Department of Chemistry, University of Podlasie, ul. 3 Maja 54, 08-110 Siedlce, Poland. kar@ap.siedlce.pl
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Karczmarzyk
mesh_terms: D003460:Crystallization / Q000379:methods; D018360:Crystallography, X-Ray; D003499:Cyclic S-Oxides / Q000138:chemical synthesis / Q000737:chemistry; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013843:Thiazines / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: C533700:3-(1-hydroxyethylidene)-2,5,7-trimethyl-2,3-dihydropyrido(3,2-e)(1,2)thiazin-4-one 1,1-dioxide; C533699:3-(hydroxy(phenyl)methyl)-2,5,7-trimethyl-2,3-dihydropyrido(3,2-e)(1,2)thiazin-4-one 1,1-dioxide; D003499:Cyclic S-Oxides; D013843:Thiazines