Angelic (AA) and tiglic acid (TA) esters are a critical pair of cis/trans isomers widely found as components of sesquiterpenes, such as humulenes and germacrenes, and are relevant for botanical dietary supplements from the Apiaceae and Asteraceae families. Due to the high similarity, it is often hard to distinguish if marker compounds possess an AA or TA ester. Accordingly, their identification requires identical reference materials for each naturally occurring ester, however this demand cannot practically be filled for such rare chemicals. The present work demonstrates that Quantum Mechanics (QM)-based NMR analysis can fulfill this unmet need by providing a qualitative and quantitative reference. The different geometry of the two isomers gives rise to small yet significant differences in the J-coupling patterns and chemical shifts, which can be determined reproducibly from 1H-NMR spectra. Thus, we demonstrate these spectroscopic differences in methyl angelate (MA) and methyl tiglate (MT) esters in CDCl3, acetone-d6 and benzene-d6 at two highly different magnetic field strengths (600 MHz and 60 MHz); DFT calculations of chemical shifts and coupling constants were also performed. Definitive knowledge of these QM numerical differences facilitates their identification and allows replacement of physical reference materials with digital data as high-level reference.