Difference Between NMR and X-Ray Crystallography

The key difference between NMR and X-ray crystallography is that NMR is an analytical technique used to determine the type and number of atoms in an organic molecule whereas X-ray crystallography is an analytical technique used to determine the atomic and molecular structure of a crystal.

The term NMR stands for nuclear magnetic resonance. This term comes under the subtopic spectroscopy in analytical chemistry. X-ray crystallography, on the other hand, is a type of crystallographic technique in which we use an X-ray beam for the analysis of crystals.

CONTENTS

1. Overview and Key Difference
2. What is NMR
3. What is X-Ray Crystallography
4. Side by Side Comparison – NMR vs X-Ray Crystallography in Tabular Form
5. Summary

What is NMR?

The term NMR in analytical chemistry indicates “Nuclear Magnetic Resonance”. This term comes under subtopic spectroscopy in analytical chemistry. NMR technique is very important in determining the type and number of different atoms in a given sample. Usually, the NMR technique is used with organic compounds. There are two main types of NMR: carbon NMR and proton NMR.

Carbon NMR determines the type and number of carbon atoms in an organic molecule. In this method, the sample is dissolved (molecule/compound) in a suitable solvent, and we can place it inside the NMR spectrophotometer. Then we can get an image or a spectrum from the spectrophotometer, which shows some peaks for the carbon atoms present in the sample. Since it is carbon NMR, we can use proton-containing liquids as the solvent because this method detects only carbon atoms, not protons.

Furthermore, carbon NMR is important in the study of spin changes in carbon atoms. The chemical shift range for 13C NMR is 0-240 ppm. To obtain the NMR spectrum, we can use the Fourier transform method. This is a fast process where a solvent peak can be observed.

Proton NMR is the other type of spectroscopic method that is useful in determining the types and number of hydrogen atoms present in a molecule. We can abbreviate it as 1H NMR. This technique includes steps of dissolving the sample (molecule/compound) in a suitable solvent and placing the sample with solvent inside the NMR spectrophotometer. Here, the spectrophotometer gives us a spectrum containing some peaks for the protons present in the sample and in the solvent as well.

What is X-Ray Crystallography?

X-ray crystallography is a type of analytical process that is important in the determination of the atomic and molecular structure of crystals. Here, the crystalline structure of the analyte causes a beam of X-rays to diffract into many specific directions.

In this process, we use a crystallographer to detect the diffracted X-rays to measure the angles and intensities of these diffracted beams, and it then produces a 3D image of the density of electrons within the crystal. The measurement of this electron density gives the position of the atoms in the crystal, allowing us to recognize the chemical bonds in the analyte and their crystallographic disorder, including various other information.

There are many materials that can form crystals: salts, metals, minerals, semiconductors and other organic, inorganic, biological molecules. Therefore, X-ray crystallography is fundamental in the development of many scientific fields.

However, there are some limitations to this X-ray crystallographic process. For example, when the repeating unit of a crystal becomes large and more complex, the image that we are getting through the crystallographer becomes less resolved. Moreover, we can perform a crystallographic process only if our sample is in crystal form.

What is the Difference Between NMR and X-Ray Crystallography?

NMR and X-ray crystallography are important analytical techniques. The key difference between NMR and X-ray crystallography is that NMR is an analytical technique used to determine the type and number of atoms in an organic molecule whereas X-ray crystallography is an analytical technique used to determine the atomic and molecular structure of a crystal.

Below infographic summarizes the difference between NMR and X-ray crystallography.

Summary – NMR vs X-Ray Crystallography

The term NMR stands for Nuclear Magnetic Resonance. X-ray crystallography is an analytical technique that uses an X-ray beam to analyze crystals. The key difference between NMR and X-ray crystallography is that NMR is an analytical technique used to determine the type and number of atoms in an organic molecule whereas X-ray crystallography is an analytical technique used to determine the atomic and molecular structure of a crystal.

Reference:

1. “X-Ray Crystallography.” Wikipedia, Wikimedia Foundation, 3 June 2020, Available here.

Image Courtesy:

1. “1H NMR Ethanol Coupling shown” By Andel – Own work, data from SDBSWeb (National Institute of Advanced Industrial Science and Technology, accessed 2019-08-03) (CC0) via Commons Wikimedia
2. “Freezed XRD” By Kaspar Kallip – Own work (CC BY-SA 4.0) via Commons Wikimedia