Question

7. (3 pts.) Shown below is the 'HNMR spectrum of curcumin in solution. In solution, curcumin could exist in diketone form or enol form, or as a mixture of the two. We can determine if the spectrum corresponds to the keto form or the enol form or a mixture of the two forms. If the spectrum corresponds to both the keto and enol form we should see the peaks for Ha protons in the keto form and the Hb proton in the enol form. Similar to the spectrum in the previous problem, the region from 6.5 - 10 ppm contains aromatic and other signals that are harder to interpret, and so you should ignore this region. H3CO. OCH3 H5CO, OCH Ha Ha HO OH Hb НО ОН الل + + + 10 1 + + 9 8 7 6 5 4 3 2 8, ppm 7a (2 pts.) By examining the NMR spectrum, you can tell that both forms for this particular diketone are not observed, only one of the two forms are present Give a BRIEF explanation why the NMR spectrum tells us that there is not mixture in this case (remember, ignore all signals in the aromatic region). 7b (1 pt.) Indicate which form is observed, the diketone or the enol, and assign the two peaks in the region 0 -6.58 (remember, the aromatic peaks and the -OH in the enol would not be observed in this region, so don't worry about them).