Experimental and theoretical studies of the tautomerism of a novel glucosyl β-diketone in solution and in the crystalline form

Abstract

This work investigates the tautomeric and conformational behavior of a carbohydrate-derived β-diketone, specifically a glucosyl-substituted 1,3-dicarbonyl compound bearing a p-methoxyphenyl group, in solution and in the crystalline phase. NMR spectroscopy in CDCl₃ reveals the predominance of an intramolecularly hydrogen-bonded enol tautomer, characterized by a strongly deshielded OH resonance at δ ≈ 16 ppm. Single-crystal X-ray diffraction shows that the compound crystallizes as a tautomeric solid solution composed of the enol form and its corresponding keto tautomer, with partial hydroxyl occupancy (∼40%), reflecting a frozen solution equilibrium. Density functional theory calculations combined with DP4+ statistical analysis support the assignment of the predominant enol tautomer in solution. These results highlight the close energetic proximity of the tautomeric forms and demonstrate the complementarity of spectroscopic, crystallographic, and theoretical approaches for elucidating the structural behavior of carbohydrate-derived β-dicarbonyl systems.