HRESI(+)MS measurements confirmed that 7a/b (C14H11Br3O8, Δmmu +0.5) and 8a/b (C14H11Br3O8, ∆mmu +0.4) were isomeric, and suggested that 9a/b (C15H13Br3O8, Δmmu +0.4) and 10 (C15H13Br3O8, Δmmu +0.5) were CH2 homologues, and 11 (C17H17Br3O8, Δmmu +0.6) was a CH2CH2 homologue of 7a/b and 8a/b. Analysis of the NMR (acetone-d6) data for 7a/b (Figures S20 and S21, Table 1, Table 2 and Table S5) confirmed them as symphyocladins C/D, first reported in 2012 from S. latiuscula as an inseparable mixture of Z/E ∆2,7′ isomers . Analysis of the NMR (methanol-d4) data for symphyocladins H/I (8a/b) (Figures S22–S27, Table 1, Table 2 and Table S6) revealed ∆2,3 and C-5 CO2Me moieties, as evidenced by diagnostic HMBC correlations (Figure 3). Significantly, these data also revealed an interconverting mixture of E/Z ∆2,3 isomers, in which the minor Z isomer, symphyocladin H (8a), as evidenced by a ROESY correlation between H2-4 and H2-7′ (Figure 3), was in equilibrium with the major E isomer, symphyocladin I (8b). Further analysis of this NMR data revealed chemical shift differences diagnostic for ∆2,3 geometric isomers; H2-4 (E δH 3.65, δC 35.0; Z δH 3.19, δC 29.5), C-1 (E δC 170.3; Z δC 166.5), C-3 (E δC 127.4; Z δC 137.8), and C-5 CO2Me (E δH 3.71; Z δH 3.51). Remarkably, the NMR (acetonitrile-d3) data for 8a/b revealed a single Z isomer 8a, as evidenced by simplified spectra, a ROESY correlation between H2-4 and H2-7′, and diagnostic chemical shifts (Figures S28 and S29, Table S7). We speculate that in aprotic solvents (i.e., acetonitrile-d3), hydrogen bonding between adjacent CO2H moieties exclusively favors the lower energy Z ∆2,3 isomer. By contrast, in protic solvents (i.e., methanol-d4), the disruption of this hydrogen bonding favor equilibration to an E/Z ∆2,3 mixture dominated by the less sterically constrained E isomer. This observation highlights the critical importance that NMR solvents can play in the analysis and structure elucidation of natural products.