CHEMISTRY 2430
Principles of Organic Chemistry I
KEY - Exam IV- 100 points - KEY

April 6, 2001 - Dr. Howard Black

1. (12 pts) Give acceptable names for the following compounds, being sure to address alkene geometry and R/S configuration where appropriate.

2. (14 pts) For each of the following four molecules, list the properties from the list on the right which best describe it. Each item on the list can be used as often as necessary, or not at all. DON'T GUESS!!
 

a. contains no sp2 carbons
b. reacts with Ag(NH3)2+ (Tollens' reagent
c. forms a salt with NH3
d. very easily oxidized, even by atmospheric O2
e. is not reduced by LiAlH4
f. incompatible with Grignard reagents
g. lowest vapor pressure of the four
h. reacts with NaBH4 to form an alcohol
i. made in one step from a 2o alcohol
j. most basic of the four molecules
k. can be formed from oxidation of a 1o alcohol

3. (30 pts) Complete the following reactions (provide either the starting molecule, the reagent(s), or product(s). If more than one product is produced, draw them all. If one product predominates, circle it.


 


 
 

4. (16 pts) Provide a synthesis of any TWO (2) of the following four molecules from the indicated starting materials. You may use any inorganic reagents you like, but all carbon atoms must come from the starting material provided. Please fill in the letter of your choices in the spaces provided on the following page.



5. (16 pts) Explain the following observations.

a. The compound illustrated in the box below has the following measurement: [a]25 = +43o. When a tiny amount of anhydrous HCl is added, the +43 number slowly declines, finally settling at 0o.

The number is the chiral compound's optical rotation.  When a small amount of acid is added, it catalyzes the formation of the enol tautomer, which is planar and thus achiral.  When the keto form then occurs, the proton can attack either side, giving either enantiomer, so racemization occurs, and there is then no optical rotation.

b. What is the effect of an electron-withdrawing substituent on the basicity of aniline? Using resonance, illustrate this effect using p-nitroaniline. Answers without at least two resonance structures will not be graded.

Electron-withdrawing groups decrease the basicity of organic bases, by
 decreasing the electron density of the nitrogen lone electron pair.  This is easily seen with p-nitroaniline, where the electron pair can be
 delocalized via resonance into the nitro group.  This resonance
 structure is also an additional one over those for just aniline.

6. (8 pts) Rank the following molecules from most acidic to least acidic, by placing the letters corresponding to each molecule in the appropriate rank supplied below.

Most acidic = 1. __C__ 2. __G__ 3. __I__ 4. __D__ 5. __F__ 6. __B__ 7. __H__ 8. __E__ 9. __A__ = Least acidic



7. (4 pts) In the box is the acid-catalyzed formation of an acetal from acetone and acidic methanol. Provide the mechanism.



Bonus(5 pts, no partial credit)
A common method for the a-bromination of simple ketones and aldehydes involves simply dissolving the substrate in acetic acid and treating it with bromine. Provide the mechanism of this straightforward reaction, as illustrated in the box.