NMR Spectroscopy - Principle, Procedure, Component, Applications
Nuclear magnetic resonance spectroscopy (NMR spectroscopy) is a technique that exploits the magnetic properties of certain atomic nuclei and can be used to determine the physical and chemical properties of atoms or the molecules in which they are contained. The technique can provide detailed information about the structure, dynamics, reaction state, and chemical environment of molecules. The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups.
When application of paramagnetic nuclear magnetic resonance
spectroscopy is not impossible, nuclear magnetic resonance spectroscopy is
usually performed on diamagnetic compounds. The nuclear magnetic resonance
spectra of inorganic compounds are often more complicated than organics because
other nuclei also have nuclear magnetic moments. Although less widespread than
the standard solution nuclear magnetic resonance spectroscopy, solid-state
nuclear magnetic resonance spectroscopy and even single-crystal nuclear
magnetic resonance spectroscopy have been used on materials that simply do not
dissolve in any solvent.
Nuclear magnetic resonance (NMR) spectroscopy is an advanced
characterization technique. It is used to determine the molecular structure at
the atomic level of a sample. Apart from the molecular structure, NMR
spectroscopy can determine phase changes, conformational and configurational
alterations, solubility, and diffusion potential.
NMR spectroscopy has been primly employed to perform
experiments on nuclei of atoms, not the electrons. The chemical environment of
typical nuclei can be mapped from the its information obtained using NMR
spectroscopy.
The fundamental concept behind NMR spectroscopy is that all
nuclei are electrically charged and have multiple spins. Under this situation,
the external magnetic field creates the possibility of an energy transfer.
Generally, this energy transfer occurs from lower to higher energy levels,
usually in a single step. This energy transfer or absorption becomes possible
at a radio frequency. Radio frequency, which is essential for the absorption of
energy, depends on three factors. It is a signature characteristic of the
nucleus type (e.g., 1H or 13C). The absorption radio frequency depends on the
chemical environment of the nucleus. It also depends on the typical nuclei
location in the magnetic field when the field is not uniform. The third factor
offers the basis to understand the concept of magnetic resonance imaging (MRI)
for coherence selection and self-diffusion coefficient measurements.
As the nuclei spin returns to its base position, the emission of energy occurs at the same frequency. This energy transfer matches with a signal, and the signal is detected in a number of ways to process and yield the same in the form of the corresponding nucleus’s NMR spectrum
What is NMR?
- Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei.
- It is a spectroscopy technique that is based on the absorption of electromagnetic radiation in the radiofrequency region 4 to 900 MHz by nuclei of the atoms.
- Over the past fifty years, NMR has become the preeminent technique for determining the structure of organic compounds.
- Of all the spectroscopic methods, it is the only one for which a complete analysis and interpretation of the entire spectrum is normally expected.
Principle of Nuclear Magnetic Resonance (NMR) Spectroscopy
- The principle behind NMR is that many nuclei have spin and all nuclei are electrically charged. If an external magnetic field is applied, an energy transfer is possible between the base energy to a higher energy level (generally a single energy gap).
- The energy transfer takes place at a wavelength that corresponds to radio frequencies and when the spin returns to its base level, energy is emitted at the same frequency.
- The signal that matches this transfer is measured in many ways and processed in order to yield an NMR spectrum for the nucleus concerned.
Procedure of Nuclear Magnetic Resonance (NMR) Spectroscopy
- The sample is placed in a magnetic field and the NMR signal is produced by excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is detected with sensitive radio receivers.
- The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups.
- As the fields are unique or highly characteristic to individual compounds, NMR spectroscopy is the definitive method to identify monomolecular organic compounds.
- Besides identification, NMR spectroscopy provides detailed information about the structure, dynamics, reaction state, and chemical environment of molecules.
- The most common types of NMR are proton and carbon-13 NMR spectroscopy, but it is applicable to any kind of sample that contains nuclei possessing spin.
Instrumentation or Component of Nuclear Magnetic Resonance (NMR) Spectroscopy
Sample holder
- Glass tube with 8.5 cm long, 0.3 cm in diameter.
Permanent magnet
- It provides a homogeneous magnetic field at 60-100 MHZ
Magnetic coils
- These coils induce a magnetic field when current flows through them
Sweep generator
- To produce an equal amount of magnetic field pass through the sample
Radio frequency transmitter
- A radio transmitter coil transmitter that produces a short powerful pulse of radio waves
Radio frequency receiver
- A radio receiver coil that detects radio frequencies emitted as nuclei relax to a lower energy level
Read out systems
- A computer that analyses and records the data.
Applications of Nuclear Magnetic Resonance (NMR) Spectroscopy
- Spectroscopy is the study of the interaction of electromagnetic radiation with matter. NMR spectroscopy is the use of the NMR phenomenon to study the physical, chemical, and biological properties of matter.
- It is an analytical chemistry technique used in quality control.
- It is used in research for determining the content and purity of a sample as well as its molecular structure. For example, NMR can quantitatively analyze mixtures containing known compounds.
- NMR spectroscopy is routinely used by chemists to study chemical structure using simple one-dimensional techniques. Two-dimensional techniques are used to determine the structure of more complicated molecules.
- These techniques are replacing x-ray crystallography for the determination of protein structure.
- Time domain NMR spectroscopy techniques are used to probe molecular dynamics in solution.
- Solid state NMR spectroscopy is used to determine the molecular structure of solids.
- Other scientists have developed NMR methods-of measuring diffusion coefficients.
References
http://chem.ch.huji.ac.il/nmr/whatisnmr/whatisnmr.html
https://www.slideshare.net/solairajananant/nmr-spectroscopy-13887430
https://www.ias.ac.in/article/fulltext/reso/009/01/0034-0049
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