Structural Significance and Reference Value of High-Precision Coupling Constants and Raw Data Sharing

While chemical shifts and J-couplings are central to ¹H NMR-based structural and metabolomic analysis, the abundance of "multiplet" designations and paucity of precisely known J_H,H values indicate that couplings are a major challenge. Fortunately, J-couplings can be determined with a precision of 0.01 Hz or better by ¹H iterative functionalized Spin Analysis (HifSA), thereby unlocking the full structural information even from complex peak patterns. This study acquired high-precision NMR spin parameters for the diastereomeric pair methyl angelate and methyl tiglate, as models for the corresponding acids, in various solvents and at two very different magnetic field strengths (60 vs 600 MHz). Determination of high-precision J value data differentiated these near-identical structural motifs with high specificity. This concept was applied to 12 naturally occurring angelates and tiglates, for which the original authors shared raw NMR data. The idea of using J values as seismographic sensors for conserved molecular geometries was also expanded to other small organic acids commonly found as natural product substituents. The collective body of evidence shows that J-couplings of geometrically conserved fragments are true constants, with only 0.02 Hz experimental variation. This allows the creation of very simple yet powerful digital reference materials (dRMs) for structural fragments, termed fragment dRMs, suitable for FAIR dissemination. The outcomes exemplify how accessible raw NMR data, coupled with advanced spin analysis, enhance structural specificity and enable structural discrimination of fragments and/or moieties across larger (metabolomic) compound sets. This once more highlights the benefits of open data practices for reproducible, high-resolution NMR analysis.