Venkat+Kavuri's+Analysis+of+the+H-NMR+of+4-methylpentan-2-one

Venkat Kavuri

4-methylpentan-2-one

URL: http://www.chemspider.com/Chemical-Structure.7621.html

Figure 1: The Complete H-NMR spectra of 4-methylpentan-2-one

Figure 1 displays the complete H-NMR spectra of 4-methylpentan-2-one. As can be seen from the spectra, there are major absorption signals to be considered.

Figure 2:H-NMR signal from methyl groups not adjacent to the carbonyl group

This absorption signal shows a doublet appearing between 0.880 and 0.960 ppm. This is due to the fact that 2 methyl (-CH3) groups are attached to the fourth carbon in 4-methylpentan-2-one. These methyl groups contain equivalent hydrogens(expected to have a signal from 0.9-1.5), which then couple with the lone hydrogen on the fourth carbon. This coupling, following the "N+1" rule produces a doublet in the spectra.

Figure 3: H-NMR signal from the hydrogens on carbons adjacent to the carbonyl group.

These absorption signals correspond to the hydrogens on the carbons adjacent to the carbonyl group. The first signal to look at is the singlet occuring between 2.080 and 2.160 ppm. This can be explained due to the fact that the first carbon on 4-methylpropan-2-one contains three hydrogens, but no coupling as there are no hydrogens on any molecules adjacent to it. This lack of coupling produces a singlet. The absorption around 2.1 is due to the fact that it is next to the carbonyl group. The second signal is a doublet, which occurs around 2.320 ppm. This signal occurs from the coupling of the 2 equivalent hydrogens on the third carbon (-CH2-) with the lone hydrogen on the fourth carbon of 4-methylpropan-2-one, following the "N+1" rule. The signal at 2.320 ppm is explained due to the fact that these hydrogens are on a carbon adjacent to a carbonyl group.