Monoterpene Unknowns Identified Using IR, 1H-NMR, 13C-NMR, DEPT, COSY, and HETCOR

Abstract

This set of NMR experiments can be a capstone experience for a spectroscopy or advanced laboratory course following organic chemistry. Students are given a monoterpene to identify using IR, 1H-NMR, 13C-NMR, and DEPT data. Once the unknown is identified, they can fully interpret and assign each carbon and each proton signal to the structure using COSY and HETCOR along with the one-dimensional NMR data. The rigidity of the ring systems and the chiral centers in all of the compounds present diastereotopic hydrogens and, in some cases, diastereotopic methyl groups. 13C-NMR clearly indicates the presence of diastereotopic methyl groups attached to a single carbon. HETCOR dramatically indicates the presence of diastereotopic hydrogen atoms on a single carbon. All but two of the compounds show at least one example of geminal coupling and five compounds show at least one example of long range coupling, either 4JW, 4Jallylic, or 4Jhomoallylic.