Hydrolyzable tannins are a class of plant polyphenols that exhibit a wide range of biological activities. 1 Among these, ellagitannins-characterized by a glucose core esterified with one or more acyl moieties such as the hexahydroxydiphenoyl (HHDP) and dehydrohexahydroxydiphenoyl (DHHDP) groups-are particularly diverse. Although numerous ellagitannins have been isolated and structurally characterized, their high structural complexity can sometimes lead to incorrect structural assignments. Accurate structural elucidation of natural products is crucial for understanding their biological functions and exploring potential therapeutic applications. Since the 2010s, DFT-based calculations of spectroscopic data have emerged as a powerful tool for both the structural elucidation and the structural revision of ellagitannins. In 2024, two macrocyclic ellagitannin dimers, 1,1′;2,2′-diHHDP-diglucose (1′) and 3,3′;4,4′-diHHDP-6,6′-digalloyl-diglucose (2′), were reportedly isolated from the wood of the sweet chestnut tree (Castanea sativa Mill.). Their proposed structures were based on 1D and 2D NMR data, as well as HR-ESI-MS measurements (Figure ). However, reexamination of the original spectroscopic data raised concerns about these assignments. In particular, the proposed dimeric structure of 2′ retained free hydroxy groups at both anomeric carbons, which would normally produce four sets of NMR signals due to α/β-anomeric forms for each of the two glucopyranose residues. Only a single set of signals was observed, suggesting different chemical structures from the originally proposed dimeric structure.