¹³C NMR

While ¹H NMR focuses on hydrogen environments, ¹³C NMR provides complementary information about the carbon skeleton. Together, ¹H and ¹³C NMR give a comprehensive picture of a molecule's framework. ¹³C NMR is particularly useful for determining how many distinct carbon environments exist and, through chemical shift values, what types of carbons are present.

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How ¹³C NMR Differs from ¹H NMR

The most common carbon isotope, ¹²C, has zero nuclear spin and is therefore NMR-inactive. Only ¹³C (spin = ½) produces an NMR signal. Since ¹³C has a natural abundance of only 1.1%, ¹³C NMR is much less sensitive than ¹H NMR — signals are weaker and require longer acquisition times or more concentrated samples.

Key differences from ¹H NMR:

Feature	¹H NMR	¹³C NMR
Natural abundance	99.98% (¹H)	1.1% (¹³C)
Sensitivity	High	Low (~1/6000 of ¹H)
Chemical shift range	0–12 ppm	0–220 ppm
Splitting in routine spectra	Yes (n+1 rule)	No (proton-decoupled)
Integration	Quantitative (proportional to number of H)	Not reliably quantitative in routine spectra

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Proton Decoupling