Write a short note on NMR

Introduction

Nuclear Magnetic Resonance is abbreviated as NMR. When placed in a high magnetic field, an NMR apparatus can see and measure the interaction of nuclear spins, allowing the molecular structure of a substance to be examined. It was shown for the first time in 1946 by Felix Bloch and Edward Mills Purcell, who later received the Nobel Prize for their achievements and study in this field.

Electron microscopes and X-ray diffraction devices can also be used to analyse molecule structure at the atomic level, although NMR has the benefit of being non-destructive and requiring minimal sample preparation.

Instrument

In block diagram, the blocks labelled N and S represent the poles of the large HO magnet, which is generally an electromagnet operated through a stabilized power supply. A field of up-to 1400 gauss and a pole of about 1.75 — 1.8 inch is necessary for high resolution spectra. The frequency and field strength are related to each other by Larmor condition.

v = үH0/2π

[This equation represents the condition of resonance.]

where HO = magnetic field,

v = is the frequency of radiation associate with transition from one state to another. It is generally known as Larmor frequency,

ү = proportionality constant or gyromagnetic ratio.

Block Diagram for NMR Spectrometer

Working Principle

The nuclear magnetic resonance (NMR) working principle is based on the spins of atomic nuclei. The term “nuclear spin” refers to nuclei having an odd mass or atomic number (in a similar fashion to the spin of electrons). A magnetic field will form around a nucleus since it is a charged particle in motion. When non-zero spin nuclei are put in a strong magnetic field with respect to the applied magnetic field and suitable energy is supplied, these nuclei flip from a lower energy state to a higher energy one. The difference in energy between the two states is determined by the applied field. The amount of energy absorbed during this transition is determined by the kind of nucleus and its chemical environment in the molecule. The magnetic field is raised, and the excitation or “flipping” of nuclei from one orientation to another is observed as an induced voltage caused by radio frequency field absorption. On Fourier transformation, the free induction decay in time domain yields its equivalent frequency domain signal. The area beneath a peak is related to the number of nuclei “flipping,” and one may learn about the structure of a molecule by examining the field strength at which protons absorb energy.

Application

NMR is a strong technology that is commonly used in Forensic Science and Biology to analyse chemicals in order to determine the molecular structure of the sample, whether it is a freshly synthesised chemical, drug, or protein, for example. Bio, foods, and chemistry are among the application sectors, as are emerging fields such as battery films and organic EL, which are improving and evolving at a rapid pace. In cutting-edge research and technological domains, NMR has become a vital analytical tool.