8. The following 1H NMR spectra represent the composition of the products submit

Question

8. The following 1H NMR spectra represent the composition of the products submitted by two groups of students after completing the Diels Alder reaction between cyclopentadiene and maleic anhydride.

a. Which product looks purer? ( 2 point)

b. What impurities appear to be present in the other sample? ( 1 point )

c. What purification technique involving a “solvent pair” might be used to purify the impure product? Briefly explain how you would carry out such a purification (experimental procedure). ( 1 point )

Explanation / Answer

The spectrum 1 looks to be purer, as it shows most of the peaks of the product, cis -norbornene-5,6-endodicarboxylic anhydride.

The two doublets t 1.5-1.7 ppm correspond to H-7 two hydrogens. The peaks at 3.4-3.6 are due to H on 3,4, 5 and 6 carbons.

The peaks at 6.1 and 6,3 should correspond t o the hydrogens on Carbons1,2 and 10 and 11.

2) The second specturm lacks many of the expected peaks. so it is more impure or has mostly the starrting materials.

3) Since the molecule is an anhydride with higher moleccular weight, we can select somewghat polar solvent like DMF or acetic acid ti dissolve all , and to separtae the product we can choose a mixture of solvents like ethylacetate+ hexane or chloroform + hexane etc.

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