If you've discovered a new protein that's never been seen before, you might not know all of its secrets yet. You might know that it has some special groups called hydroxyl and sulfur groups, but you might not know where they are or how the protein is shaped. That's where NMR spectroscopy comes in. By using NMR spectroscopy, you can figure out where those groups are and how the protein is shaped.

In this article, we're going to talk about NMR spectroscopy. We'll start by explaining what it is and how it works. Then, we'll talk about how to read the results of an NMR spectroscopy test. Finally, we'll talk about all the different ways that NMR spectroscopy is used by scientists every day. So, if you're interested in science and want to learn more about NMR spectroscopy, keep reading! And don't worry, we'll explain everything in simple terms that anyone can understand.

How does NMR spectroscopy work?

NMR spectroscopy relies on some tricky concepts, but the process itself is relatively simple. You follow these steps:

Dissolve your sample in a suitable solvent, such as .Add a small amount of a reference molecule, such as TMS.Place the sample in an external magnetic field.Fire radio waves at the sample. NMR spectroscopy, short for nuclear magnetic resonance spectroscopy, is an analytical technique we use primarily to find out the structure of molecules. It is based on the behaviour of certain nuclei in an external magnetic field. Nuclei in the sample absorb and emit radio waves according to the other atoms or groups bonded to them. These waves are detected by a detector. The detector produces a spectrum showing the energy absorbed against a property called chemical shift.

What is chemical shift?

To understand NMR spectroscopy, we need to talk about something called chemical shift. NMR spectra show the chemical shift of nuclei, which is measured in parts per million, or ppm.

When certain nuclei are placed in an external magnetic field, they can take one of two states: spin-aligned or spin-opposed. If we give them enough energy, they can flip from one state to the other. This energy is called their magnetic resonance frequency.

But here's the interesting part: magnetic resonance frequency varies depending on the environment of an atom. An atom's environment is all the different chemical groups attached to it. Identical nuclei from the same element can have different magnetic resonance frequencies and different chemical shift values if they are bonded to different groups. That's why only nuclei with odd mass numbers can be used in NMR spectroscopy; they have a property called spin. In Understanding NMR, you'll learn more about how this works and why it's so important for NMR spectroscopy.

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Interpreting NMR spectra

As we mentioned above, NMR spectroscopy produces graphs called spectra, plotting energy absorbed by the sample against chemical shift. The graphs show a number of different peaks. Nuclei from identical atoms produce peaks at different chemical shift values depending on the other atoms or groups of atoms bonded to them. Notice the peak shown at 0 ppm. This is given by TMS, a reference molecule. Tetramethylsilane, also known as TMS, is a molecule commonly used as a reference point in NMR spectroscopy.

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There are two important things to know:

Environments with certain functional groups produce chemical shift peaks that fall within a particular range.Unique environments give unique chemical shift peaks. How does this help us? Well, if you have two clear peaks on your spectrum, your sample must contain nuclei in two different environments. You can then compare the chemical shift value of the peaks to values in a data book, which will tell you what sort of environment the nuclei are in, and the different functional groups that are attached to them. This helps you work out the structure of the molecule in your sample. Let’s say you have the following spectrum for an unknown molecule.

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You can see peaks at around 58 ppm, 18 ppm and 9 ppm. Let’s compare these values to a data table.

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The peak at 58 ppm matches the values for an  group, which range from 50-90 ppm. We can therefore infer that this molecule contains that particular group. Similarly, we can see that the peak at 18 ppm falls into the range for an  group, and the peak at9 ppm falls into the range for an  group. What molecule do you know that contains just these particular groups? Let’s put them together:

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The molecule is propan-1-ol. In summary, by comparing chemical shift values to ranges in a data book, we can infer the different groups within a molecule and work out its overall structure.

Different types of NMR spectroscopy

Not all nuclei can be used in NMR spectroscopy. Most aren’t influenced by an external magnetic field and can’t be detected. Two types of nuclei that do produce results in NMR spectroscopy are carbon-13 nuclei and hydrogen-1 nuclei. Remember that carbon-13 shows that we have an isotope of carbon with a mass number of 13. Mass number is the combined number of protons and neutrons in an atom. Carbon has an atomic number of 6, meaning it has six protons, and so carbon-13 atoms must have 13 - 6 = 7 neutrons. Both types of spectroscopy follow the general technique described above and detect the chemical shift of carbon-13 nuclei and hydrogen-1 nuclei respectively.  However, the chemical shift peaks in hydrogen-1 spectra fall within a much smaller range. Hydrogen-1 NMR spectroscopy is also known as proton spectroscopy. A hydrogen-1 nucleus doesn’t have any neutrons or electrons - it is just a proton.

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Hydrogen-1 NMR spectroscopy does have some advantages over carbon-13 spectroscopy:

Most hydrogen atoms are the isotope hydrogen-1, whereas only about 10 percent of carbon atoms are the isotope carbon-13. This means that hydrogen-1 spectra give clearer, more distinct results. The size of peaks in hydrogen-1 spectra is proportional to the number of hydrogen-1 nuclei in that particular environment, which isn’t the case for carbon-13 NMR peaks. This is shown using an integration trace.Hydrogen-1 peaks show something called spin-spin coupling. This is where they split into smaller peaks depending on how many hydrogen atoms are in adjacent environments, and it gives us further information about the molecule's structure.

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You’ll learn more about carbon-13 and hydrogen-1 NMR in  Carbon -13 NMR and Hydrogen -1 NMR respectively.

Using NMR spectroscopy

NMR spectroscopy has many applications in modern science. As we’ve explored, its primary function is analysing molecule structure and shape. However, it is also used for the following purposes: Determining protein folding. Drug screening and design. Finding out how molecules interact in chemical reactions. Determining the proportion of solids and liquids in lipids. Pros and cons of NMR spectroscopy, NMR Spectroscopy has both pros and cons. Let's consider them below.

Benefits

Its spectra are unique, well-resolved, and generally predictable for smaller molecules. It produces distinguishable signals for different functional groups.It can even be used to distinguish the same functional group in different environments.

Limitations

NMR spectroscopy is an analytical technique that can determine the shape and structure of molecules. To carry out NMR spectroscopy, you dissolve your sample in a solvent and add a reference molecule called TMS. Then, you place the sample in a magnetic field and fire radio waves at it. A detector produces a graph of energy absorbed against a property called chemical shift.

The environment of a nucleus, which includes all the different atoms and groups of atoms surrounding it, affects its chemical shift value. By comparing chemical shift values to data book ranges, you can identify the functional groups present in a molecule.

The two most common types of NMR spectroscopy are carbon-13 NMR and hydrogen-1 NMR. Hydrogen-1 NMR spectroscopy provides more information about the environments of the nuclei it detects through integration traces and spin-spin coupling.

While NMR spectroscopy produces unique and well-resolved spectra that can distinguish between different functional groups and environments in a molecule, it has some limitations. It requires large sample sizes, expensive machines, and can only be used for soluble substances. It is also a slow process and cannot be used for fast reactions.

NMR Spectroscopy

What is NMR spectroscopy?

NMR spectroscopy is an analytical technique used to determine molecule shape and structure. It is based on the behaviour of certain nuclei in an external magnetic field.

How do you read NMR spectra?

You read NMR spectra by comparing peaks, which show chemical shift, to values in a data book. These tell you the functional groups present in your sample molecule.

What does NMR spectroscopy measure?

NMR spectroscopy measures the chemical shift of nuclei. This is a property related to magnetic resonance frequency, the energy needed to flip a nucleus from its antiparallel state to its parallel state.

What are the uses of NMR spectroscopy?

NMR spectroscopy is used to find molecule structure and shape, determine how proteins fold, identify molecules, and help design drugs.

What is chemical shift in NMR spectroscopy?

Chemical shift is a property related to magnetic resonance frequency, which is the energy needed to flip a nucleus from its antiparallel state to its parallel state. Nuclei from atoms of the same element have different chemical shift values depending on the other chemical groups attached to them.

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