Sections of 2D ¹H-¹³C 700 MHz NMR spectra of a sialyl Lewis x–capped glycan in D₂O. In this example, the combination of heteronuclear single quantum coherence (HSQC) and HSQC-total correlation spectroscopy (TOCSY) spectra is used to assign the chemical shift of each peak to an atom in the structure. Each residue in the structure is delineated by Roman numerals, and atom numbers in each residue are denoted using Arabic numerals. Assigning ¹H-¹³C crosspeaks is accomplished by correlating data in the HSQC (top panel) and the HSQC-TOCSY (bottom three panels). The HSQC shows a peak for every ¹H atom covalently bonded to a ¹³C atom. The HSQC-TOCSY shows crosspeaks for all ¹Hs in a ring (also called a spin system) connected to a particular ¹H-¹³C crosspeak. For example, the bottom panel shows connections for the anomeric pairs of I-Gal (4.38 ¹H ppm, 102.6 ¹³C ppm) and II-GlcNAc (4.72 ¹H ppm, 102.51 ¹³C ppm). Along each of the horizontal dotted lines are the ¹H chemical shifts for the ¹Hs in a ring, annotated as I4, I3, and I2 for I-Gal and II4, II2, and II3 for II-GlcNAc. The positions are characteristic of a residue type and linkage. Once the residue is identified the peaks in the HSQC can be assigned. The resulting assignments can be used in subsequent three-dimensional structure determination.