Question

How is the peak affected in `C^13 NMR` by the number of H's attached to the carbon?

Answer 1

In a "normal" `""^13"C"` NMR spectrum, the number of `"H"` atoms attached to the carbon does not affect the peak.

That's because most `""^13"C"` NMR spectra are broadband decoupled .

The couplings are removed by applying a continuous second radio signal that excites all the protons and cancels out their couplings with the `"C"` atoms.

Thus, the spectrum of 2-bromobutane consists of four singlets.

However, there is a technique called off-resonance decoupling , in which only the protons bonded to a given carbon atom split its signal.

Thus, a `"CH"_3` group appears as a quartet, a `"CH"_2` group appears as a triplet, a `"CH"` group appears as a doublet, and a quaternary `"C"` appears as a singlet.

So, the off-resonance decoupled spectrum of 2-bromobutane consists of two quartets, a triplet, and a doublet.