Matthew Marthaler
March 16, 2012
Instrumental Lab
Laboratory 6: FT-NMR Laboratory
Introduction:
In this lab, I will be working with Fourier Transform Nuclear Magnetic Resonance (FT-NMR) and
becoming more familiar with its uses and techniques. NMR measures the absorption of electromagnetic
radiation in the radio-frequency region of roughly 4 to 400 MHz. The nuclei of atoms rather than the
electrons are involved in the absorption process. In FT-NMR, nuclei in a strong magnetic field are
subjected periodically to very brief pulses of intense RF radiation whose length is usually less than 10 us
with a frequency of 102 to 103 MHz. The free-induction decay (FID) signal is excited by the excited nuclei
as they relax. The FID signal is digitalized and stored in a computer for data processing. The data is
converted into a frequency domain signal by a Fourier Transformation and digital filtering may be
applied to the data to further increase the signal-to-noise ratio. In easier terms, the sample is placed in a
strong magnetic field and the nuclei affected by the field can be investigated.
Purpose:
The ultimate purpose of this procedure is to determine the structures of organic compounds.
For the first day, we will be running standard and unknown organic compounds on the FT-NMR. We will
also start proton (measures H’s) and C13 (measures carbons) of samples. For day two, we will finish
proton and C13. We will then run a 2D analysis of the samples.
Procedure:
Day One
1) Make standards from Crisco pure vegetable oil, Planters peanut oil, Pompeian extra virgin
olive oil, Stearic acid, and Palmitic acid.
2) The make the samples of the three oils, place 4 drops of the oil in an NMR tube and then put
chloroform in the tube until the liquid reaches 4 – 4.5 cm.
3) To make the acid samples, place 0.08 g in an NMR tube and then put chloroform in the tube
until the liquid reaches 4 – 4.5 cm.
4) Run standard samples on the NMR (S.O.P in my notebook).
5) Pick unknown A or B and run it.
6) Begin Proton and C13 of the samples.
Day Two
1)
2)
3)
4)
Run standard samples on the NMR.
Pick unknown A and run it.
Do proton and C13 analysis on the samples.
Run 2D analysis of the samples.
Results:
Chemical Structures of the Standards
Stearic Acid
Palmitic Acid
Crisco Pure Vegetable Oil
+ oil =
Planters Peanut Oil
+ oil =
Pompeian Extra Virgin Olive Oil
+ oil =
1H Proton Analysis for Our Standards and Unknowns
Stearic Acid
Chemical Shift
Integration
0.9
1.278
1.654
2.366
35.85
35.85
35.85
2.30
Carbon Chain - 5
Planters Peanut Oil
Chemical Shift
Integration
0.897
1.276
1.617
1.638
2.044
2.089
2.319
2.777
4.141
4.293
4.812
5.351
7.281
68.68
68.68
68.68
68.68
68.68
14.52
14.52
1.89
1.87
1.81
3.98
7.25
n/a
Carbon Chain - 33
Crisco Pure Vegetable Oil
Chemical Shift (ppm)
5.344
4.178
4.158
2.774
2.291
2.316
1.260
Integration
9.84
1.95
1.96
3.91
5.97
9.82
66.56
Carbon Chain - 52
Extra Virgin Olive Oil
Chemical Shift (ppm)
5.358
4.815
4.319
4.162
2.777
2.320
1.309
Integration
6.16
2.33
1.80
1.90
0.69
5.63
81.48
Carbon Chain - 35
Unknown A
Chemical Shift
Integration
0.889
1.276
1.385
1.639
1.736
2.046
2.321
2.778
4.143
4.280
4.816
5.331
7.281
65.99
65.99
65.99
65.99
65.99
9.35
5.73
3.25
1.87
1.86
3.09
8.86
n/a
Carbon Chain - 39
From our calculations, I believe that the unknown is a mixture of Crisco vegetable oil and Planter’s
peanut oil. This is, because the Carbon chain length is close to the number of Carbons in the peanut oil.
Also, the integration numbers on the unknown came up to look like the integration numbers for Crisco
vegetable oil and Planter’s peanut oil.
Calculations
Percent errors for Carbon Length:
Stearic Acid:
Peanut Oil:
5−18
18
33−30
30
Vegetable Oil:
Olive Oil:
x 100 = 72.22% error
52−51
35−18
18
x 100% = 10% error
51
x 100% = 1.96% error
x 100 = 94.44% error
Conclusion
In conclusion, we were able to run both C13 APT and 1H Proton analysis on our standards and
compounds, but we were not able to run a 2D analysis (not enough time). We made the samples by
putting the desired amounts of chloroform and our sample/standard directly into the NMR tube, but
later found out this was not the way to prepare samples (there was no mention of how to prepare the
samples in the S.O.P though and we did not know this was an inaccurate way of making them). We then
tested stearic acid and Palmitic acid first, followed by vegetable, peanut, and olive oil, and then we ran
our unknown. We ran out of time to get a 1H Proton analysis for Palmitic acid, but that was the only
sample we missed. Our results came out adequately, but the 1H Proton spectra for the different oils
came out with numerous chemical shift values. This could be due to the oils having numerous signals,
our improper way of making the samples, improper shimming, or to excess noise. We were still able to
read the chemical shift and integration numbers for our standards and samples though, even with this
problem. We calculated the percent error for the Carbon lengths and some came out well and others
did not. This could be due to the fact that some samples were made better than others (less chloroform,
mixed better, correct amount of sample), the instrument works better for different samples, or the
noise was better for different samples. From our calculations, I believe that the unknown is a mixture of
Crisco vegetable oil and Planter’s peanut oil. This is, because the Carbon chain length is close to the
number of Carbons in the peanut oil. Also, the integration numbers on the unknown came up to look
like the integration numbers for Crisco vegetable oil and Planter’s peanut oil.
If anything could be changed to the experiment, it would be to have a proper explanation of
how to make the samples and have the instruction manual or experts give a brief review on how to
interpret the data. Overall this lab was more frustrating than others (because of the long time to run
each sample and it coming up with poor results), but it still helped me gain a grasp on how to run the
NMR.