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  •  » Identify 4-methylpentan-2-one from the IR and NMR spectra

#1 2010-04-26 18:15:06

orgopete
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Identify 4-methylpentan-2-one from the IR and NMR spectra

Can you identify the unknown from the following NMR and IR spectra?

This appears to be a student NMR. As such, it lacks the detail to enable easier interpretation. However, there is sufficient detail to identify the compound as it is a fairly simple structure.

The integral is imprecise, but we can apply simple thinking here. It appears that there is a doublet(?) (2.3 ppm), singlet (2.1 ppm), and doublet (0.9 ppm). The compound is not an ester or ether with a CH-O-bond by the lack of a chemical shift greater than 3 ppm.

The IR contains a C=O peak and the peaks at 2+ ppm are consistent with CH-groups attached to a C=O. However, it is difficult to think of an arrangement that will give a 1H doublet, a 2H singlet, and a 3H doublet. We should try an alternate by doubling the integral values. That will give a 2H doublet, a 4H singlet, and a 6H doublet. A four hydrogen singlet is not possible, but this singlet does not look clean. It looks as though a multiplet could be hidden within it.

If we assume this to be the case, then a structure that would fit would be as follows. The 6H doublet is the isopropyl group, the two groups near 2 ppm are alpha to the C=O group. The missing CH-multiplet splits the CH2 and CH3 groups into doublets. This CH group broadens the singlet and increases the integral to 4H.


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