*4.3.4.3.1 Proton broadband decoupling*

*Phytochemicals in Human Health*

**Figure 3.** *1*

**Figure 4.**

or the carbon spectrum, the absorption peaks generated by the general compounds appear in the lower field than TMS, that is to say, *δ* values generated by common com-

techniques that assist in structural analysis, such as selective decoupling, heavy hydrogen exchange, addition of reaction reagents, and dual irradiations.

13C-NMR spectra can provide structural information of organic compounds, including the number, types, and chemical environment of carbon atoms [27]. It is one of the important means for the structural identification of organic compounds.

or the molecules contain several quaternary carbon atoms, 13C-NMR spectra will provide crucial information for the structure identification. The chemical shifts of

Common 13C-NMR techniques include proton broadband decoupling, off resonance decoupling (OFR), insensitive nuclei enhanced by polarization transfer (INEPT), and distortionless enhancement by polarization transfer (DEPT). Proton broadband decoupling and DEPT spectra are most commonly used at present.

*4.3.4.3 Carbon nuclear magnetic resonance spectroscopy (13C-NMR)*

Especially, where there are serious signal peak overlaps in the 1

common carbon signals are shown in **Figure 4** [4].

H-NMR spectrum is mostly in the range

H-NMR spectrum,

H nuclei are shown in **Figure 3** [4].

H-NMR spectrum technique, there are some auxiliary

pounds is positive. The chemical shifts of the 1

*H-NMR chemical shift range of common hydrogen protons.*

of *δ*0–20. Some typical chemical shifts of 1

*13C-NMR chemical shifts of common carbon signals.*

In addition to the normal 1

**62**

Proton broadband decoupling spectrum is measured after 1 H nuclei are saturated with broadband electromagnetic radiation. At this point, the couplings between 1 H and 13C are completely eliminated, and all 13C signals are shown as singlets, so it is very convenient to determine the chemical shift of 13C signals. In addition, because of the NOE effect of 1 H after irradiation, the signal of 13C signal connected with 1 H will be increased, while the quarterly carbon signal will show weak absorption peaks.
