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Nuclear Magnetic Resonance Spectroscopy, abbreviated as NMR Spectroscopy, is defined as the study of molecules by recording the interaction of radiofrequency electromagnetic radiations with the nuclei of molecules being placed in a strong magnetic field. The strange behaviour of certain nuclei, when placed in a strong magnetic field, was first observed by a Dutch Physicist, Zeeman at the end of the nineteenth century and was so-called the `Zeeman effect’. There are different types of spectroscopy and NMR spectroscopy is one of them. Let’s learn NMR spectroscopy in detail and discuss some important questions.
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Keywords: NMR Spectroscopy, Magnetic Field, nuclei, atoms, molecules, 1H NMR, 13C NMR
What is NMR Spectroscopy?
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Nuclear Magnetic Resonance Spectroscopy abbreviated as NMR Spectroscopy is a research tool for organic chemists which can determine both the physical and chemical properties of atoms or molecules. The NMR Spectroscopy relies on the phenomenon of nuclear magnetic resonance and provides detailed information about the structure, reaction state, and chemical environment of molecules.
Basis of NMR Spectroscopy
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Nuclear Magnetic Resonance (NMR) Spectroscopy was first detected experimentally by a workgroup, Felix Bloch from Stanford University and Edward Purcell from Harvard University at the end of the year 1945. Later, in the year 1952, both Bloch and Purcell were jointly awarded the Nobel Prize in physics for their research on Nuclear Magnetic Resonance (NMR) Spectroscopy.
- Nuclear Magnetic Resonance (NMR) Spectroscopy is a crucial research analytical tool for organic chemists. It is said that with the aid of the NMR spectroscopy, the research in the organic lab has been drastically improved. The NMR spectroscopy can not only provide information on the structure of the molecule but can also determine the content and purity of the given sample. 1H NMR and 13C NMR are known to be the most widely used NMR.
Principle of NMR Spectroscopy
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NMR Spectrospe’s principle is based on the fact that all nuclei are electrically charged and the nuclei of most of the atoms show spin. The nuclei of most of the atoms have spin and are electrically charged so that they can generate magnetic fields. In the presence of an external magnetic field, transfer of energy is possible from the ground state to the excited state. The transfer of energy occurs at a wavelength that matches with radio frequencies. Also, when the energy returns to the ground state from an excited state, it is known to emit the radio wave of the same frequency. This emitted radio frequency gives the NMR spectrum.
NMR Spectroscopy Principle
Working of NMR Spectroscopy
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The working of NMR Spectroscopy is shown in the following steps mentioned below:
- First, we need to place the given sample in a magnetic field.
- Then, we need to excite the nuclei sample into nuclear magnetic resonance with help of radio waves to produce NMR signals.
- These produced NMR signals are then detected with sensitive radio receivers.
- The resonance frequency of an atom in a molecule is changed by the intramolecular magnetic field which surrounds it.
- This then gives detailed information about a molecule’s functional group and also its electronic structure.
Nuclear Magnetic Resonance (NMR) Spectroscopy is a definite method of identifying monomolecular organic compounds and it also provides detailed information about the structure, dynamics, reaction state, and chemical environment of a molecule.
Instrumentation of NMR Spectroscopy
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The instrumentation of NMR Spectroscopy consists of nine major parts and they are explained below as follows:
- Sample Holder – It is generally a glass tube which is about 8cm long and 0.3 cm in diameter.
- Magnetic coils – They are used to generate a magnetic field whenever current flows through it.
- Permanent magnet – It is used to provide a homogenous magnetic field.
- Sweep generator – It is used to modify the strength of the magnetic field.
- Radiofrequency transmitter – It helps in producing a powerful but short pulse of radio waves.
- Radiofrequency receiver – It helps in detecting or receiving radio frequency signals.
- RF detector – It helps in determining and receiving unabsorbed radio frequency signals.
- Recorder – It helps in recording the NMR signals which are received by the RF detector.
- Readout system – It is a computer which is connected to the system to analyze and record the data.
NMR Spectroscopy Instrumentation
Applications of NMR Spectroscopy
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The various applications of NMR Spectroscopy are mentioned below as follows:
- It is used by chemists and biochemists to identify the properties of organic molecules.
- It is used to analyze mixtures containing known compounds.
- It is used to determine the molecular structure of different compounds
- It is used to check the clarity and purity of given samples.
- It is used in the study of various drugs.
- It is used in food science.
Points to Remember
- Nuclear Magnetic Resonance Spectroscopy is abbreviated as NMR Spectroscopy.
- NMR Spectroscopy is defined as the study of molecules by recording the interaction of radiofrequency electromagnetic radiations with the nuclei of molecules being placed in a strong magnetic field.
- NMR Spectroscopy was first detected experimentally by a workgroup, Felix Bloch from Stanford University and Edward Purcell from Harvard University at the end of the year 1945.
- NMR Spectroscopy can provide detailed information about the structure, reaction state, dynamics and chemical environment of molecules.
- NMR Spectrospe’s principle is based on the fact that all nuclei are electrically charged and most of them show spin.
- NMR Spectroscopy is used to check the clarity and purity of given samples.
- NMR Spectroscopy is used to determine the molecular structure of different compounds
- (Proton) 1H NMR and (Carbon) 13C NMR are known to be the most widely used NMR.
Sample Questions
Ques: Define NMR Spectroscopy. [3 Marks]
Ans: Nuclear Magnetic Resonance (NMR) Spectroscopy is defined as the study of molecules by recording the interaction of radiofrequency electromagnetic radiations with the nuclei of molecules being placed in a strong magnetic field. It is a research analytical tool for organic chemists which can be used to determine both the physical and chemical properties of molecules.
It is generally a research tool for organic chemists which can determine both the physical and chemical properties of molecules. The NMR Spectroscopy relies on the phenomenon of nuclear magnetic resonance and provides detailed information about the structure, reaction state, dynamics and chemical environment of molecules.
Ques: State the principle of NMR Spectroscopy. [1 Mark]
Ans: The principle of NMR Spectroscopy states that all nuclei are electrically charged and the nuclei of most of the atoms show spin.
Ques: Define chemical shift in NMR Spectroscopy. Also, state the different nuclei that can be detected by NMR spectroscopy and which of them are most widely used? [3 Marks]
Ans: Chemical shift in NMR Spectroscopy is defined as the difference between the resonant frequency of the spinning protons and the signal of the reference molecule. NMR chemical change is one of the most important properties.
The different nuclei that can be detected by NMR spectroscopy are as follows: 1H (proton), 13C (carbon), 15N (nitrogen), 19F (fluorine) and many more.
1H and 13C are the most widely used among them.
Ques: What is Proton NMR used for? [1 Mark]
Ans: Proton nuclear magnetic resonance (1H NMR) is a technique usually used to determine the structure of molecules.
Ques: What is the difference between 1H NMR and 13C NMR? [2 Marks]
Ans: The difference between 1H NMR and 13C NMR are as follows:
- 1H NMR is used to determine the number of hydrogen atoms in a molecule whereas, 13C NMR is used to determine the carbon atoms in a molecule.
- 1H NMR usually has a slow process whereas, 13C NMR is much faster.
Ques: What are the various NMR Spectroscopy Techniques? [2 Marks]
Ans: The various NMR Spectroscopy techniques are as follows:
- Resonant frequency
- Acquisition of Spectra
- Sample handling
Ques: What is the size limit for NMR? [1 Mark]
Ans: The size limit for NMR is approximately equal to 35kDa (kilodaltons).
Ques: State the major parts used in NMR Spectroscopy? [4 Marks]
Ans: The major parts used in NMR Spectroscopy are as follows: Sample Holder, Magnetic coils, Permanent magnet, Sweep generator, Radiofrequency transmitter, Radiofrequency receiver, RF detector, Recorder, and Readout system.
Ques: State the limitations of NMR Spectroscopy and ways to overcome them. [4 Marks]
Ans: The limitations of NMR Spectroscopy are as follows:
- Sensitivity – NMR Spectroscopy may be a versatile technique but it often fails due to its low sensitivity. It’s a huge disadvantage while examining complex reactions. To overcome the low sensitivity, one can use advanced hardware.
- Magnetic Field Drift – Drift in the magnetic field is known to have a huge impact on NMR Spectroscopy, leading to twisted lineshapes. To overcome this, one can make certain corrections in the magnetic field while recording the measurement.
Ques: Why is carbon tetrachloride used in NMR? [1 Mark]
Ans: Carbon tetrachloride is used in NMR because it does not contain any proton. Hence, it does not disturb the most widely used 1H NMR absorption.
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