The 13C NMR spectra normally are recorded with simultaneous 1H broad-band decoupling. For this reason in the proton-decoupled 13C spectrum (the JCH couplings disappear) all the carbon nuclei give single peaks.
Broadband decoupling
However, if the molecule contains other magnetic active nuclei such as 19F, 31P, 2H etc the proton-decoupled 13C NMR spectrum will show coupling to these nuclei. The broad-band 1H decoupling yields an increase of up to 200 % in the signal intensities through the NOE (nuclear Overhauser effect).
13C-19F splitting patterns
It should be noted that, the values for scalar couplings (JCH) between 1H and 13C, and the carbon signal multiplicity can give additional information for the structure determination. The disadvantages of proton-coupled 13C spectra are the decreased sensitivity due to the distribution of the signal intensity into the different lines of the multiplet, the signal overlap, and the missing NOE effect.
Proton - coupled 13C spectrum (expansion)
Proton - coupled 13C spectrum (expansion 1)
Proton - coupled 13C spectrum of C-3
Proton - coupled 13C spectrum of C-6
Proton - coupled 13C spectrum of C-7
Proton - coupled 13C spectrum of C-18
Proton - coupled 13C spectra of C-4, C-7, and C-8
Proton - coupled 13C spectrum
The gated-decoupled 13C spectrum is recorded with 1H decoupling during the relaxation delay, whereas the decoupling is switched off during 13C acquisition.
Gated decoupling
For the inverse gated-decoupling experiment the 1H decoupling is active during the acquisition, whereas it is switched off during the relaxation delay. The sensitivity improvement due to the NOE-effect is suppressed for this experiment and thus the acquired spectrum can be integrated. Note that there is a build up of the NOE-effect during the acquisition period when decoupling is active. In order to suppress this NOE-effect the relaxation delay must be 10-times the T1 relaxation time for 13C.
Inverse Gated decoupling
Proton - coupled 13C spectrum (no nOe)
