Chemistry Workshops

for Organic Chemistry

1. Your task is to identify the structure of an unknown compound that has the formula C5H8O2 .
You will test it with the following, in this order :

a) IR
b) LiAlH4
c) K2Cr2O7
d) C-13 NMR

Once you determine what possible observations might result from each of the tests and what conclusions you could draw, your workshop leader will tell you the results of each test.

2. Optically active compound A (C5H10O) decolorizes cold dilute permanganate and upon hydrogenation (H2/Pt) gives optically inactive compound B (C5H12O). When A is reacted with chromic acid (K2Cr2O7, aqueous H2SO4) at room temperature, optically inactive compound C is formed. Give structures A-C consistent with this information.

3. Write a complete mechanism that explains the following conversion. Assume there is no water present, i.e., the ketal does not hydrolyze to a ketone.

4. Compounds A and B have the formula C5H11Cl. Neither A nor B react with NaI in acetone or with NaSCH3 in dimethylsulfoxide with any appreciable rate. B also does not react with NaOCH2CH3 in dimethylsulfoxide at an appreciable rate. In contrast, A reacts with NaOCH2CH3 in dimethylsulfoxide to give compounds C and D, which both have formula C5H10 and IR bands between 1650-1660 cm-1. The H NMR spectra of A and C are tabulated below.

Propose structures for A-D that are consistent with the experimental observations.

H NMR (A): 1.01 ppm, 3H, triplet ; 1.51 ppm, 6H, singlet ; 1.73 ppm, 2H, quartet

H NMR (C): 1.57 ppm, 3H, doublet ; 1.60 ppm, 3H, singlet ; 1.68 ppm, 3H, singlet ; 5.17 ppm, 1H, quartet

5. Three compounds, A, B, and C, were all optically active, all had strong IR bands in the 1700 cm-1 region and all gave precipitates D, E, and F, respectively, with 2,4-dinitrophenylhydrazine reagent. When A was treated with NaOD/D2O, three hydrogens were exchanged for deuterium (D) and the deuterated A remained optically active. When A was treated with I2/aq. NaOH, a yellow precipitate (G) and H formed. Compounds B and C did not give a yellow precipitate with I2/aq. NaOH. Compound B exchanged only one H for D when treated with NaOD/D2O, and the monodeuterated B was now optically inactive. When compound C reacted with NaOD/D2O, four H's were exchanged for D's and the deuterated C remained optically active. Give structures for A-H consistent with the above information. (There may be more than one structure possible for either A, B, or C.)