John Siller
Laboratory 7
FTNMR
Introduction:
Nuclear Magnetic Resonance Spectroscopy (NMR) is an analysis technique that uses a strong
magnetic field to provide detailed information about the structure and properties of molecules. In NMR
a super-cooled conducting wire generates a strong magnetic field. Molecules react differently based on
their own magnetic field created by the movement of their nuclei and electrons. High frequency
electromagnetic radiation probes the molecules which react differently depending on their structure
and properties. A detector measures the resulting electromagnetic radiation and computer software is
used to compare the two signals and convert the difference from the time domain. Using NMR
spectroscopy it is easy to identify and count the number of unique protons and carbons in a molecule.
Different scans for different atomic isotopes may be performed as long as the isotope has a spin factor
of +/- ½. The most common scans are 1H and 13C. In this lab both scans were run on two unknowns,
labeled unknown A and B, and two samples of oil. The oil samples were peanut and extra virgin olive oil.
The NMR has been previously used in Organic and Physical chemistry so we have had a good amount of
experience on it compared to other instruments in the lab.
Method:

















Mix 4 drops of sample with 4 cm of chloroform in an NMR test tube
Open Topspin program
Type ej to eject place holder
Place NMR tube on feeder and type ij
Type ro on to start the rotation of the sample
Type new and input parameters
Select the proper solvent and experiment type
Type rsh to select shim file
Type lock to lock magnet
Type bsmsdisp to start the shimming program
Adjust z, z2, and z3 to adjust shim
Type eda to open parameters
Type zz to acquire spectrum and wait for all scans to be complete
Type ft to Fourier Transform the spectrum
Type apk to peak pick
Type abs to adjust the baseline and integrate peaks for analysis
Type ej to eject the sample and replace it with placeholder.
Results:
1
H proton and 13C APT spectra for both unknowns and both oils can be found in my lab
notebook. Peanut oil is made up of mainly oleic acid, linoleic acid, and palmitic acid. The structure of
these acids consists of a long chain of carbons and hydrogens with a carboxyl group at the end. These
acids differ in the number of double bonds found within the long chain of carbons. Olive oil also consists
of these oils but with a different ratio. The NMR spectra of these oils shows the large number of carbons
in the chain as well as any functional groups that might be found in trace amounts compared to the
main three oils. Trying to identify the two different unknowns is rather difficult due to the similar
structures of their spectra. The unknowns can clearly be identified as containing similar molecules to
both the peanut oil and olive oil analyzed in this lab. The spectra are practically identical for all four of
the oils analyzed. First looking at the 13C spectra, the first thing that jumps out is the cluster of multiple
peaks between 20 and 40 ppm. This region of the spectra arises from the long chain of sp3 hybridized
carbons found in the backbone of the molecules that make up the oils. Some peaks are observed in the
aromatic region of the spectra. These peaks can be explained by antioxidants, such as vitamin E, that are
added to improve the shelf life of peanut and olive oil. It is interesting to note the difference in peaks
found in this region when comparing peanut to olive oil. It appears that peanut oil has two strong peaks
in this region where olive oil only has one. This could be an indication of the fact that more things are
added to peanut oil than extra virgin olive oil. It would be interesting to analyze a number of possible
additives on the NMR and determine which correspond to these peaks. The peaks in the range between
50 and 75 ppm are due to the carbons that make up the carboxyl croup at the end of the long backbone
chain. Looking at the proton spectra is useful for determining the saturation of the carbon backbone of
the molecule. If each acid was isolated and run through the NMR the peaks would be easier to
distinguish between, but with the mixtures that were analyzed in this lab there is not much that can be
identified by the proton spectra other than the presence of both saturated and unsaturated oils.
Conclusion:
The FTNMR is a powerful instrument comprised of a powerful magnet that is very useful in the
analysis of chemical structures of molecules. This lab was fairly informative on the makeup of oils used
and consumed every day in cooking. It was very interesting to learn the details of the chemical
structures that make up the molecules in cooking oil. This lab was very nice compared to some of our
other labs that produced outlandish results or were not able to be completed due to instrumentation
error and incapacity. We were able to analyze all of the samples we wanted to and were only limited by
the time it takes to perform the 13C APT scans. The longer time it takes to run carbon scans opposed to
hydrogen scans stems from the low abundance of 13C compared to 1H in molecules. The NMR is a very
complex instrument and it can be used in a wide variety of ways which we barely scraped the surface of.
There are a large number of variables that can be changed in NMR spectroscopy including solvents,
temperatures, scans, and what isotope is being identified. These variables results in a multitude of
different experiments that can all be run on one powerful instrument. The NMR is also very nice to use
because you can set up the experiment or scans that you’re trying to run, and then let the instrument do
its thing without the need for further human input. Experiments can be run over long periods of time
assuming no one else needs to use it, which is not often the case in our busy lab. Our NMR is constantly
being run during the day by a variety of classes and individuals. This clearly shows the importance and
usefulness of such a powerful instrument.