Nikul Patel
Analysis of H-NMR Spectrum of Pinacolone (3,3-dimethyl-2-butanone)
Pinacolone spectra obtained from http://science.widener.edu/svb/nmr/known_jdx.html.

The molecular formula of pinacolone is (CH3)3CCOCH3. The molecular structure of pinacolone can be seen below.

Structure.JPG
Structure of Pinacolone

Pinacolone_main_(inverted_numbers).JPG
Figure 1: H-NMR Spectrum of Pinacolone


The figure above (Figure 1) shows the H1-NMR spectrum of 3,3-dimethyl-2-butanone or more commonly, pinacolone. As you can see from the figure, there are two different peaks present and each peak corresponds to a different type of proton. The size of each peak indicates how many of each type of proton are present in the molecule. According to the structure of pinacolone seen at the top of the page, there is a single carbon double bonded to an oxygen (carbonyl group) with one methyl group and one t-butyl group on either side of the carbon. From the figure, the signal corresponding to the protons on the methyl group is smaller than the signal corresponding to the protons on the t-butyl group. This is because there are only three protons in the methyl group and nine protons in the t-butyl group. As predicted from this information, the above picture of the complete spectrum of pinacolone shows two different signals, each corresponding to the two different protons.

Pinacolone_large_peak.JPG
Figure 2: Enlarged Peak Produced by Protons of t-Butyl Group


The above figure (Figure 2) shows the signal produced by the protons of the t-butyl group. According to the accepted chemical shift values for the various types of protons in HNMR, these specific protons should produce a signal within the range of 0.9-1.5 ppm. As expected, there is a signal at approximately 1.15 ppm. Furthermore, each of the nine protons on the t-butyl group are all equivalent, meaning that they do not couple with each other. Not only that, but there is no splitting between these protons and the other protons of the molecule because they are directly bonded to a carbon that is next to a carbonyl group that does not have any protons. In other words, the other protons within this molecule do not influence the signal produced by these protons. Thus a signal with one peak is produced.

Pinacolone_smaller_peak.JPG
Figure 3: Enlarged Peak Produced by Protons of Methyl Group


The above figure (Figure 3) shows the signal produced by the protons on the methyl group. These methyl protons should produce a signal around 2.1 ppm as is common of protons attached to a carbon that is next to a carbonyl group. According to the figure, a single peak appears at around 2.15 ppm, which coincides with the expected signal. Moreover, the protons on the methyl group are all equivalent, so they do not couple with one another. Like for the protons on the t-butyl group, the methyl protons are not split by any other protons since they are next to a carbonyl group that does not have any protons on it. Therefore, like the protons on the t-butyl gruop, the protons on the methyl group produce a signal with a single peak.

[The analysis is good JCB]

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