Download Chem 322 Exam 2 April 16, 2012 /100 Name Please do the easiest

Chem 322
Exam 2
April 16, 2012
/100
Name
Please do the easiest questions first; ask for clarification of any item.
1. (3 each) Draw the structure of:
a. 5-(3-chloro-4-nitrophenyl)-1-pentene
b. Z-3-cyclopentyl-2-pentenal
c. 2-methylpropyl butanoate
2. (3 each) Name according to IUPAC rules (ignore chirality):
3. Attack of excess CH3MgI at 0 °C on 2-butanone and propanoyl chloride proceeds by different pathways to
give different kinds of products.
a. (3) What path is followed during attack on 2-butanone? Show the mechanism.
b. (3) What path is followed during attack on propanoyl chloride? Show the mechanism (first step only).
c. (3) Explain why different paths are followed.
4. (12) You must determine which one of the following 4 compounds is in an unlabeled bottle: butanoic acid,
butanal, 1-butanol, 2-butanone. Design a set of chemical tests that would permit you to accurately identify the
mystery liquid. Present a decision tree (I suggest left-to-right on the page) on which you write the sequence of
tests you would apply and what you would know if the outcome is positive and if it is negative for each test in the
sequence.
5. (6) What instrumental method could you use to instantly tell whether an unknown was an aldehyde or a
ketone? What tell-tale feature of the instrument’s output would you look for and what would its presence or
absence tell you?
6. (10) Complete the “roadmap”:
7.a. (4) Show how to synthesize 4-bromo-3-nitrobenzoic acid from toluene and any other needed reagents.
7.b. (10) Show how to synthesize the compound below from benzene, alcohols of 4 C or fewer, and any inorganic
reagents.
8. (4) Explain mechanistically why benzylic hydrogens are much easier to replace with Br under free radical
conditions than most other kinds of H.
9. Predict all products that would be recovered in significant amounts for the following reactions. Write “NR” if
there is no reaction. (3 pt each)
Chem 322
Exam 2
April 16, 2012
/100
Name
Grading Key
Please do the easiest questions first; ask for clarification of any item.
1. (3 each) Draw the structure of:
a. 5-(3-chloro-4-nitrophenyl)-1-pentene
b. Z-3-cyclopentyl-2-pentenal
c. 2-methylpropyl butanoate
2. (3 each) Name according to IUPAC rules (ignore chirality):
2-benzyl-1-chloropentan-3-one
N,2-diethylbenzamide
3. Attack of excess CH3MgI at 0 °C on 2-butanone and propanoyl chloride proceeds by different pathways to
give different kinds of products.
a. (3) What path is followed during attack on 2-butanone? Show the mechanism.
Grignard adds to carbonyl C forcing one pair of electrons from the C=O to the O, making it a C–O-. There is no
good leaving group on the former C=O.
b. (3) What path is followed during attack on propanoyl chloride? Show the mechanism (for the first step only).
Grignard adds to carbonyl C as above, but since Cl- is a good leaving group, an electron pair from the –O- reforms the C=O as Cl- departs.
c. (3) Explain why different paths are followed. In (a) there are no good leaving groups on the carbonyl C, so we
have a simple addition to it. In (b) there is a good LG, so we see a nucleophilic addition followed by an
elimination. Thus the first step of this reaction looks like a substitution.
4. (12) You must determine which one of the following 4 compounds is in an unlabeled bottle: butanoic acid,
butanal, 1-butanol, 2-butanone. Design a set of chemical tests that would permit you to accurately identify the
mystery liquid. Present a decision tree (I suggest left-to-right on the page) on which you write the sequence of
tests you would apply and what you would know if the outcome is positive and if it is negative for each test in the
sequence. Several variations of the sequence below would work.
5. (6) What instrumental method could you use to instantly tell whether an unknown was an aldehyde or a
ketone? What tell-tale feature of the instrument’s output would you look for and what would its presence or
absence tell you?
Proton nmr would be the choice. Look for a peak worth one H around 9 ppm. If present you have an aldehyde; if
absent you have a ketone.
6. (10) Complete the “roadmap”:
7.a. (4) Show how to synthesize 4-bromo-3-nitrobenzoic acid from toluene and any other needed reagents.
Combine toluene with Br2/FeBr3; discard the ortho product. Treat the p-bromotoluene with hot alkaline KMnO4
to oxidize the methyl to a carboxyl (follow with acidic workup). Finally, treat the product with HNO3/H2SO4 to
nitrate at the 3 position (carboxyl directs meta; Br directs ortho – so these two cooperate).
7.b. (10) Show how to synthesize the compound below from benzene, alcohols of 4 C or fewer, and any inorganic
reagents.
8. (4) Explain mechanistically why benzylic hydrogens are much easier to replace with Br under free radical
conditions than most other kinds of H.
If Br· abstracts a benzylic H, the unpaired electron on the resulting benzylic radical can be delocalized around
the ring, appearing on C2,4,6. This delocalization reduces the energy needed to create the odd electron.
9. Predict all products that would be recovered in significant amounts for the following reactions. Write “NR” if
there is no reaction. (3 pt each)
salt (anilinium propanoate)
dehydration is spontaneous
because of extensive resonance
2-bromotoluene plus 4-bromotoluene
Sulfonate is removable by aq. acid hydrolysis
benzaldehyde
(imine)
NR (ring is deactivated by attached C=O, so no Friedel-Crafts is possible)
Methyl acetate (ester) plus acetic acid
Propanoic acid