Analysis of 4-methyl-pentan-2-one using NMR
By Laura Ramirez
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Figure 1: Skeletal Structure of 4-methyl-2-pentanone
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Figure 2: H-NMR Spectrum for 4-methyl-2-pentanone


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Figure 3: This figure shows a doublet between 0.880 and 0.960 ppm. This doublet is a result of the coupling interaction that occurs between the hydrogens on adjacent carbons on the fourth and fifth carbons. The first peak located at around 0.910 ppm and the second peak located at about 0.940 ppm falls within the carbon-hydrogen interactions that are expected for a shielded CH3 group, which is 0.9-1.2 ppm. The doublet is observed because of the coupling interaction between the single hydrogen on the fourth carbon and the hydrogens on the methyl group of the fourth carbon and the fifth carbon.


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Figure 4: This figure shows a singlet between 2.120 and 2.160 ppm. This peak corresponds to the hydrogens on the first carbon of the compound. Coupling interactions do not occur with the hydrogens on the first carbon because the protons are too far from the hydrogens on the third carbon. Deshielding of the hydrogens is observed in this figure because of the carbon-oxygen double bond on the second carbon. The observed ppm range is within the expected ppm range for a proton deshielded by a carbonyl group, which is 2.0-2.2 pmm.

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Figure 5: This figure shows a doublet between 2.280 and 2.360 ppm. This doublet is the result of coupling interaction between the hydrogens of the third carbon and the hydrogen on the fourth carbon. The first peak at around 2.300 ppm and the second peak at around 2.325 ppm are the result of deshielding by the carbon-oxygen double bond found on the second carbon. This is slightly higher than the expected deshielding range, but it still supports that deshielding of the protons by a carbonyl group took place.


Reference:
Bramer, S.E. (1996). Inherent properties, identifiers, and references: 7621. Retrieved on March 16, 2009 from the ChemSpider website: http://www.chemspider.com/Chemical-Structure.7621.html.