Chemistry Chem 216 H, Exam 2 - University Of Michigan printable pdf download

Chemistry Chem 216 H, Exam 2 - University Of Michigan

Name_______Key___________________

216 H W12-Exam No. 2

Page 2

I. (16 points) Show how many peaks you would expect to observe in the proton-decoupled

C NMR spectra

of the following compounds. Indicate your answers in the boxes provided.

II (14 points) Consider the relative Rf values of the compounds shown in the following reaction scheme

when analyzed by thin-layer chromatography (TLC) on silica gel-coated plates.

(1) (2 points) Which one should show the lowest Rf among all of the compounds 1 through 5?

Answer ____4______

(2) (2 points) Which of compounds 1 and 2 should show a higher Rf?

Answer ____1______

(3) (2 points) Which of compounds 1 and 3 should have a higher Rf?

Answer ____1______

(4) (2 points) Which of compounds 2 and 3 should have a higher Rf?

Answer ____3______

(5) (2 points) Which of compounds 2 and 5 should have a higher Rf?

Answer ____5______

(6) (2 points) Compound 1 is shown to have a high Rf value (~0.8) when a mixture of 3 : 1 ethyl

acetate/hexanes is used as an eluent. How would you change the solvent system in order to have a

considerably lower Rf value for this compound?

Answer:

__Increase the fraction of hexanes in the solvent mixture or use hexanes

alone___

(7) (2 points) Separation of a mixture of compounds 1, 2 and 4 by silica gel column chromatography is

attempted using an organic solvent system such as a mixture of hexanes and ethyl acetate. Which of these

three compounds is likely to be eluted from the column first?

Answer ____1______

Chemistry Chem 216 H, Exam 2 - University Of Michigan