NMR: How it Works and Applications

This document provides an overview of nuclear magnetic resonance (NMR) spectroscopy, explaining its working principle and applications. It discusses how NMR can be used to determine molecular structure, bond lengths, and angles, as well as the local coordination environment. The document also explores the different techniques used in NMR and the concept of chemical shift. Additionally, it includes a 1H NMR spectrum and explains how it can be used to identify the molecular structure of a compound.

Running Head: NMR
NMR
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Q1
How NMR works
This is nuclear Magnetic resonance spectroscopy. It is a method used to study molecules of
different substance where the following information about a molecule can be obtained.
Diffusion coefficient, 2D and 3D image of the molecule, protein structure, molecular structure,
bond lengths and angle and the local coordination environment (pg. 2). It is a method that is
used in quality control and research when determining the purity and content of the samples
along with the molecular structure. All nuclei have a property known as a spin. The spin
numbers start from 0 and increase infinitely at rate of 0.5 depending on the atom. Each spin
has a given energy level and moment (pg. 3).
When determining the unknown compounds, the content is always weighed against the
content in the library. After determining the basic structure from the library, this method can
then be used to determine the molecular conformation as well as studying the physical
properties. Among the physical qualities include the solubility, phase change, diffusion and
conformational change. There are various techniques used in NMR (pg 4).
The energy emitted is given by
Δ E=h vl
Where Δ E is the energy change Vl if the Larmor frequency
Q2

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Large molecules have large electrons surrounding the nucleus and therefore has a large shift
(pg. 11). 1H has smaller chemical shift compared to all other am=toms since its has only one
electron. Below is a diagram showing the chemical shoft range of a hydrogen comapared to a
carbon atom (pg. 12).
Figure 1: Chemical shift for the 1H compared to that of a carbon atom in benzene ring.
If a molecule is being tested, the first thing is to subject it to the NRR. The frequency of the
energy emitted after the electromagnetic radiation is compared with what is kept in the library.
However, if the molecule is total new, a different approach is where the nearest known
spectrum is used and compared closely. Taking for instance it is a methanol molecule, the
molecule resonates at a chemical shift that is lowest. The phenyl group donates the electron
and therefore has the highest chemical shift. Aromatics has electro positivity that has a
resonance between 4-5 ppm (pg. 14).

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Nuclei have a spin and they contain electric charge. When subjected to a magnetic field, there is
energy transfer between one energy level to another (pg.12). The transfer takes places at radio
frequencies of radio waves after which there is an energy that is emitted at the same
frequency. The emitted energy signal can then be measured in several ways and processed to
determine the nucleus concerned.
Q3
Here is a 1H NMR spectrum what molecular does it come from?
For a molecule X that has say chemical shift between 0.5-1 ppm, and has the following
characteristics (pg. 19).
Figure 2: Characteristics of molecule x
The mark x in blue in the figure indicate the location of the unknown x molecule.
The range of ppm suggest that its either an alkane or a methyl group. However the value 3
indicates it has intensity level of 3 that is associated with methyl groups (pg. 20).

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