Resumen de Synthesis and 1H NMR Spectroscopic Elucidation of Five- and Six-Membered d-Ribonolactone Derivatives
Eric S. Sales, Gustavo P. Silveira
Lactone-size identification of d-ribonolactone derivatives has been debated for four decades due to complex lactone-ring rearrangements and acetal migration. This laboratory experiment for an upper-division undergraduate organic chemistry laboratory course describes a fast and reliable assignment of lactone-size derivatives from d-ribose using 1H and 1H–1H NOESY NMR spectroscopy. In addition, the further derivatization of these lactones via O-acylation is described, followed by a theoretical study that allows conformational analysis of these molecules in solution using JANOCCHIO software. Overall, this experiment uses simple, inexpensive, and commercially available reagents, and the reactions are performed in mild conditions. The products are solid and can be either purified by crystallization or used directly in the next step of the synthesis. 13C, 2D 1H–1H COSY, and 1H–13C HMQC or HSQC spectra are also analyzed. Therefore, this laboratory experiment allows students to explore several NMR techniques and relate them with basic NMR concepts, such as scalar coupling constants related to dihedral angles and the NOE effect, to predict lactone-size and conformation of the synthesized molecules in solution.
