title: Distinguishing tautomerism in the crystal structure of (Z)-N-(5-ethyl-2,3-dihydro-1,3,4-thiadiazol-2-ylidene)-4-methylbenzenesulfonamide using DFT-D calculations and (13)C solid-state NMR.
abstract: The crystal structure of the title compound, C11H13N3O2S2, has been determined previously on the basis of refinement against laboratory powder X-ray diffraction (PXRD) data, supported by comparison of measured and calculated (13)C solid-state NMR spectra [Hangan et al. (2010). Acta Cryst. B66, 615-621]. The molecule is tautomeric, and was reported as an amine tautomer [systematic name: N-(5-ethyl-1,3,4-thiadiazol-2-yl)-p-toluenesulfonamide], rather than the correct imine tautomer. The protonation site on the molecule's 1,3,4-thiadiazole ring is indicated by the intermolecular contacts in the crystal structure: N-H...O hydrogen bonds are established at the correct site, while the alternative protonation site does not establish any notable intermolecular interactions. The two tautomers provide essentially identical Rietveld fits to laboratory PXRD data, and therefore they cannot be directly distinguished in this way. However, the correct tautomer can be distinguished from the incorrect one by previously reported quantitative criteria based on the extent of structural distortion on optimization of the crystal structure using dispersion-corrected density functional theory (DFT-D) calculations. Calculation of the (13)C SS-NMR spectrum based on the correct imine tautomer also provides considerably better agreement with the measured (13)C SS-NMR spectrum.
authors.affiliation: Department of Pharmacy, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark.
authors.forename: Xiaozhou
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Pharmacy, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Bond
authors.affiliation: Department of Pharmacy, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark.
authors.forename: Kristoffer E
authors.initials: KE
authors.lastname: Johansson
authors.affiliation: Department of Pharmacy, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark.
authors.forename: Jacco
authors.initials: J
authors.lastname: Van de Streek
keywords: NMR analysis; amine–imine tautomerism; crystal structure; dispersion-corrected DFT; powder diffraction
references.citation: Acta Crystallogr B. 2010 Dec;66(Pt 6):615-21
references.pmid: 21099024
references.citation: Acta Crystallogr B Struct Sci Cryst Eng Mater. 2014 Feb;70(Pt 1):72-80
references.pmid: 24441130
references.citation: Cryst Growth Des. 2013 Jan 2;13(1):19-23
references.pmid: 23378823
references.citation: Angew Chem Int Ed Engl. 2011 Aug 16;50(34):7924-6
references.pmid: 21744444
references.citation: J Comput Chem. 2006 Nov 30;27(15):1787-99
references.pmid: 16955487
references.citation: IUCrJ. 2014 Feb 28;1(Pt 2):136-50
references.pmid: 25075330
references.citation: Acta Crystallogr B. 2002 Jun;58(Pt 3 Pt 1):380-8
references.pmid: 12037359
references.citation: Inorg Chem. 2013 Apr 15;52(8):4431-42
references.pmid: 23544767
references.citation: Acta Crystallogr B. 2010 Oct;66(Pt 5):544-58
references.pmid: 20841921
references.citation: Phys Rev Lett. 1996 Oct 28;77(18):3865-3868
references.pmid: 10062328
references.citation: J Phys Chem C Nanomater Interfaces. 2013 Jun 13;117(23):12258-12265
references.pmid: 24386493
references.citation: J Pharm Sci. 2012 Nov;101(11):4214-9
references.pmid: 22886472
references.citation: Chemistry. 2013 Mar 11;19(11):3552-7
references.pmid: 23401016
references.citation: J Am Chem Soc. 2010 Mar 3;132(8):2564-6
references.pmid: 20136091