Resumen de Complete Assignment of Proton Chemical Shifts in Terpenes:: An Experiment Combining 2D NMR Spectroscopy with Molecular Modeling
COSY spectroscopy of a set of four bicyclic[3.1.1]terpenes is described. The rigid carbon framework gives dihedral angles of nearly 90° for several adjacent protons which results in very small coupling constants for those protons. The rigid framework also results in W-coupling between the two non-adjacent bridgehead protons. The unexpected coupling which is shown clearly in the COSY spectrum can be illuminated by molecular modeling of the terpenes. Thus students learn both to use COSY spectroscopy to assign peaks in the 1H spectrum of a terpene but also to use the results from molecular mechanics calculations to understand the results from unusual geometries.
