Fig. 7: Deciphering the atom connectivity in altered structures through combined HMBC (400 MHz) and HSQC (900 Mhz) NMR.
From: Advancing lignin analytics via elucidation of linkage progressions in lignin populations
Top left (A): Complete HMBC NMR demonstrating atom connectivity by through bond correlations. Purple coded: the aldehyde proton connectivity to Cβ, Cα in allylic structures, typically appearing in the region 13C: 125.0-130.0 ppm, and C1 aromatic typically around 13C: 128.0-130.0 ppm. Blue coded: the aromatic proton attached to C2 correlates with aromatic carbons C1, typically at 13C: 128.0 ppm, C3 and C4, typically at 13C: 145.0-152.0 ppm, and Cα in ketone, typically at 13C: 190.0-210.0 ppm. Pink coded: previously analyzed Hibberts ketone as reported from model studies by Miles-Barett et al. 34 is also detected. Top Right (A*): Zoom in of the aromatic, allylic and aldehyde regions of the HMBC. Signals of specific interest are marked and color-coded. Bottom left (B): 2D-HSQC NMR with noted signals relevant for HMBC analysis. Bottom right: Classification of altered structures detected in this work. Description of used symbols and previously analyzed ketones, also detected in this work.
