Prevalence of the thioamide {⋯H-N-C=S}2 synthon - solid-state (X-ray crystallography), solution (NMR) and gas-phase (theoretical) structures of O-methyl-N-aryl-thiocarbamides

Abstract

Structural investigations, i.e. solid-state (X-ray), solution ( 1H NMR) and gas-phase (theoretical), on molecules with the general formula MeOC(=S)N(H)C6H4-4-Y: Y = H (1), NO2 (2), C(=O)Me (3), Cl (4) have shown a general preference for the adoption of an E-conformation about the central C-N bond. Such a conformation allows for the formation of a dimeric hydrogen-bonded {⋯H-N-C=S}2 synthon as the building block. In the cases of 1-3, additional C-H⋯O interactions give rise to the formation of tapes of varying topology. A theoretical analysis shows that the preference for the E-conformation is about the same as the crystal packing stabilisation energy and consistent with this, the compound with Y = C(=O)OMe, (5), adopts a Z-conformation in the solid-state that facilitates the formation of N-H⋯O, C-H⋯O and C-H⋯S interactions, leading to a layer structure. Global crystal packing considerations are shown to be imperative in dictating the conformational form of molecules 1-5. © The Royal Society of Chemistry 2005.