Question

Why won't you see any carbon-carbon splitting in `C^13 NMR`?

Answer 1

Because the isotopic abundance of the carbon-13 nucleus is around 1%.

Explanation:

In simple terms, let's look at ethane, `H_3C-CH_3`.

Approximately 1% of the sample will contain a spin active carbon nucleus. Approximately 1% of this 1% will contain 2 spin active carbon nuclei. Such absorptions due to these isotopomers will likely disappear into the baseline (be weaker than the intensity of the background noise), as they are not significantly abundant.