ANSWER KEY

SPRING 1999

FINAL EXAM, 130AL

MOUSER, 6/7/99

2. Dibenzyl ketone had a higher Rf value and thus is more polar.

As one rotates about the C-C bond separating the carbonyl groups, the individual carbonyl dipoles cancel reducing the net dipole of the molecule. Experimental data suggest that this cancellation is great enough so that the dipole of benzil is less than that of Dibenzyl ketone.

3.

4. (15 points) 1000 mg of caffeine dissolves in 46 mL of water or 5.5 mL of chloroform. 200 mg of caffeine is added to 10.0 mL of water. This solution is extracted two times with a 5 mL volume of chloroform. SHOW YOUR WORK FOR CREDIT

5.

a.

b.

c.

6. MgSO₄ complexes (or "ties up") the water more so than Na₂SO₄. [MgSO₄ forms a stronger complex with water.]

7. (20 points) Complete the below detailed mechanism for the aldol experiment carried out in lab (show all arrow pushing).

+3 points for arrow pushing for each step; + 2 points for equilibrium arrows; -1 point for each wrong charge assignment; — 5 points for wrong structure (or for not defining "R" group).

8.

9. time required for a compound to come off the column; increase; increase; decrease

10. 4, 5, 11, 10

11. Toluene was too good of a solvent. Good solvation prevents the component from interacting with the stationary phase. Pooor interacts results in poor separation. [Effectively, the solvent shell prevents the stationary phase from "seeing" the different dipoles.]

12.

+ 5 Points

Spectrum #1 has methylene chloride in it. [Student #1 did not do a good job in boiling off all the extracting solvent, methylene chloride.]

+ 5points

A, the OH stretch is dilute

+ 5points

B, C-H stretch of methylene chloride

C, C-H bend of methylene chloride (subtle, give full credit even if this peak is not designated).

D, C-Cl stretch of methylene chloride

13.

14.