Carbon-13 is an NMR-active nucleus with low natural abundance. Its magnetogyric ratio is smaller than that of protons, making carbon-13 resonance weaker than proton resonance. Carbon-13 chemical shifts appear between 0 and 220 ppm, a much larger range than that seen in protons. For this reason, non-equivalent carbons have distinct and well-resolved signals that do not overlap. Like proton chemical shifts, carbon-13 chemical shifts are influenced by hybridization, magnetic anisotropy, and electronegativity. While two bonds separate protons from electronegative substituents, the directly attached carbon-13 atom is strongly deshielded. Saturated carbons appear upfield near the TMS signal at zero ppm, followed by those attached to electronegative substituents. Unsaturated and aromatic carbons appear further downfield, followed by highly deshielded carbonyl carbons.