Main Difference – 1H NMR vs 13C NMR
The term NMR stands for Nuclear Magnetic Resonance. It is a spectroscopic technique used in analytical chemistry for the determination of content, purity and the molecular structures present in a sample. It gives us information about the number and the types of atoms present in a particular molecule. The basis of NMR is the use of magnetic properties of atomic nuclei. NMR is one of the strongest tools that can be used to determine the molecular structure of organic compounds. There are two common types of NMR: 1H NMR and 13C NMR. The main difference between 1H NMR and 13C NMR is that 1H NMR is used to determine the types and number of hydrogen atoms present in a molecule whereas 13C NMR is used to determine the type and number of carbon atoms in a molecule.
Key Areas Covered
1. What is NMR
– Basis of NMR, Chemical Shift
2. What is 1H NMR
– Definition, Features, Examples
3. What is 13C NMR
– Definition, Features, Examples
4. What is the Difference Between 1H NMR and 13C NMR
– Comparison of Key Differences
Key Terms: Atomic Nuclei, Carbon, Magnetic Properties, NMR, Proton
What is NMR
Basis of NMR
All atomic nuclei are electrically charged (due to the presence of protons). Some atomic nuclei have a “spin” around their own axis. When an external magnetic field is applied, an energy transfer is possible; with the spinning, the atomic nuclei goes to a high energy level from a base energy level. This energy transfer corresponds to a radio frequency, and when the spin comes back to the base energy level, this energy is emitted at the same frequency as a signal. This signal is used to yield an NMR spectrum for that atomic nuclei.
Chemical Shift
Chemical shift in NMR is the resonance frequency of a nucleus relative to the standard. Different atomic nuclei give different resonance frequencies depending on the electronic distributions. The variations in NMR frequencies of the same kind of nuclei due to differences in electronic distributions is known as the chemical shift.
What is 1H NMR
1H NMR is a spectroscopic method used to determine the types and number of hydrogen atoms present in a molecule. In this technique, the sample (molecule/compound) is dissolved in a suitable solvent and is placed inside the NMR spectrophotometer. Then the equipment will give a spectrum showing some peaks for the protons present in the sample and in the solvent as well. But the determination of protons present in the sample is difficult due to the interference coming from the solvent protons. Therefore, a suitable solvent that does not contain any protons should be used. Ex: deuterated water (D2O), deuterated acetone ((CD3)2CO), CCl4, etc.
Figure 1: A 1H NMR for Ethyl Acetate
Here, the peaks given by different hydrogen atoms are given in different colors.
The chemical shift range of 1H NMR is 0-14 ppm. In obtaining the NMR spectra for 1H NMR, continuous wave method is used. However, this is a slow process. Since the solvent does not contain any protons, 1H NMR spectra have no peaks for the solvent.
What is 13C NMR
13C NMR is used to determine the type and number of carbon atoms in a molecule. Here also, the sample (molecule/compound) is dissolved in a suitable solvent and is placed inside the NMR spectrophotometer. Then the equipment will give spectra showing some peaks for the protons present in the sample. Unlike in 1H NMR, proton containing liquids can be used as the solvent since this method detects only carbon atoms, not protons.
Figure 2: 13C NMR for benzene. Since all the carbon atoms are equivalent in the molecule, this NMR spectra gives only one peak.
13C NMR is the study of spin changes in carbon atoms. The chemical shift range for 13C NMR is 0-240 ppm. To obtain the NMR spectrum, can use Fourier transform method. This is a fast process where a solvent peak can be observed.
Difference Between 1H NMR and 13C NMR
Definition
1H NMR: 1H NMR is a spectroscopic method used to determine the types and number of hydrogen atoms present in a molecule.
13C NMR: 13C NMR is a spectroscopic method used to determine the types and number of carbon atoms present in a molecule.
Detection
1H NMR: 1H NMR detect proton nuclei.
13C NMR: 13C NMR detects carbon nuclei.
Chemical Shift Range
1H NMR: The chemical shift range of 1H NMR is 0-14 ppm.
13C NMR: The chemical shift range of 13C NMR is 0-240 ppm.
Method
1H NMR: In obtaining the NMR spectra for 1H NMR, continuous wave method is used.
13C NMR: To obtain the NMR spectrum, can use Fourier transform method.
Progression
1H NMR: 1H NMR process is slow.
13C NMR: 13C NMR process is fast.
Solvent Peak
1H NMR: 1H NMR spectra do not give a solvent peak.
13C NMR: 13C NMR gives a solvent peak.
Conclusion
NMR is a spectroscopic technique used to determine the different forms of atoms present in a given molecule. There are two types of NMR techniques named as 1H NMR and 13C NMR. The main difference between 1H NMR and 13C NMR is that 1H NMR is used to determine the types and number of hydrogen atoms present in a molecule whereas 13C NMR is used to determine the type and number of carbon atoms in a molecule.
Reference:
1. Hoffman, Roy. What is NMR? 3 May 2015, Available here.
2. Raju Sanghvi, pharmacist Follow. “COMPARISION BETWEEN 1 H & 13 C NMR.” LinkedIn SlideShare, 20 Sept. 2014, Available here.
Image Courtesy:
1. “1H NMR Ethyl Acetate Coupling shown” By 1H_NMR_Ethyl_Acetate_Coupling_shown.GIF: T.vanschaikderivative work: H Padleckas (talk) – This file was derived from1H NMR Ethyl Acetate Coupling shown – 2.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Benzene c13 nmr” By DFS454 (talk) – (CC BY-SA 3.0) via Commons Wikimedia
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