(CHE 325) Organic Chemistry II
Spring 2011
EXAM #2
Name:
KEY
ID#:
Check your exam to be sure it is complete. There are seven questions in this exam. It
is worth 100 points. Read each question carefully, and answer in clearly legible and
coherent English. Use the back of the page for additional space if needed (clearly
indicate on the front of the page that you have done so). Partial credit will be given, so
show your work. Don't fall in love with individual problems. Do the ones first which you
can do easily. Pace yourself. Do your own work. Good luck!
N. Totah
.
1.
(of 10)
2.
(of 12)
3.
(of 8)
4.
(of 9)
5.
(of 36)
6.
(of 10)
7.
(of 15)
Total:
(100)
Name:
1. (10 points) Give IUPAC names for the following compounds:
a.
O
H
OCH3
2-methoxyhexanal
b.
S
ethyl isopropyl sulfide
c.
O
OH
3,4-e poxy-3-methylbutan- 1-ol
d.
O
HO
H CH3
(S)-2-hydroxypentan- 3-one
2
Name:
2a. (4 points) Rank the following compounds in order of decreasing acidity. Rank the
most acidic compound 1, and the least acidic compound 4.
OH
NO2
OH
OH
NMe2
OH
CH3
4
1
2
3
2b. (4 points) Rank the following compounds in order of decreasing boiling point. Rank
the highest boiling compound 1, and the lowest boiling compound 4.
CH3CH2CH2CH2-OCH3
OH
CH3 CH2CH2CH2 CH2
O
CH3O CH2 C CH3
CH3
CH3 C CH2 CH3
CH3
3
1
2
4
2c. (4 points) Rank the following compounds in order of decreasing reactivity to
nucleophilic addition. Rank the most reactive compound 1, and the least reactive
compound 4.
O
O
H
1
O
O
H
Cl
3
4
3
2
Name:
3. (8 points) Explain the following observations using mechanistic arguments. For full
credit, show key reactive intermediate(s) and clearly indicate how each set of
products is formed.
a. When butyl methyl ether is treated with HI and heat, the products of the reaction
are mainly methyl iodide and butanol. Little or no methanol or butyl iodide are
formed.
This reaction proceeds via an S N 2 m echanism.
After protona tion of ethe r oxygen, iodi de attacks the
least hindered position
CH3
O
HI
CH3
CH3
H
O
CH3
OH
+
CH3 I
CH3
I
b. When tert-butyl methyl ether is treated with HI and heat, the only products formed
are tert-butyl iodide and methanol.
This reaction proceeds via an S N 1 m echanism.
After protonati on of the ether oxygen, methanol lost to
generate more stable 3° carb ocati on.
Iodide then traps the cati on forming t -butyl iodide.
CH3
CH3
O
CH3
CH3
HI
CH3
CH3
H
CH3
CH3
O
I
+
CH3
CH3
CH3
CH3
CH3
4
CH3
CH3 OH
I
Name:
4a. (6 points) Propose structures for the following fragments found in the Mass
Spectrum of tert-butanol (MW = 74). Identify the type of fragmentation that results
in formation of each of these two ions.
m/z
Ion Fragment
M (74)
59
CH3
Type of Fragmentation
CH3
C OH
CH3
none (parent ion)
α cleavage
CH3
CH3 C OH
CH2
56
dehydrati on
CH3 C
CH3
4b. (3 points) Clearly explain how you could distinguish between the compounds
shown below by 1H NMR. For full credit, note what you would expect to see for each
compound. Be specific. Cite numerical values/ranges as needed to support your
claims.
CH3CH2 O CH2CH3
CH3CH2 OH
A
B
Compound B will show a broad singlet (δ 1.0 - 5.0) that
corresponds to the OH proton.
Compound A will not.
Note: it is not possible to distinguish the two by integration!
5
Name:
5. (36 points) Predict the major product(s) for the following reactions. Assume
reagents are present in excess amounts unless otherwise indicated. Clearly depict any
stereochemistry. "No Reaction" is a possible answer. CAUTION! Don't confuse
reactions that will occur slowly with those that will not occur!
a.
H
OH
Cl
SOCl2
H
b.
O
1. OsO4, pyridine
2. HIO4
O
(step 1)
product(s)
of step 1
OH
1. NaBH4
2. H3O+
OH
(step 2)
c.
O
OH
PCC
O
OH
CH2Cl2
O
O
H
6
Name:
d.
mCPBA
(1 equiv.)
O
e.
O
O
(CH3CH2CH2)2CuLi
Cl
f.
1. Mg0
Br
OH
2. H2C=O
3. H3O+
(step 1)
product(s)
of step 1
O
1.
Hg(O2CCF3)2
2. NaBH4
(step 2)
g.
OH
POCl3
pyridine, 0°C
7
Name:
h.
OH
Na2Cr2O7
CH3CO2H (aq), heat
No Reaction
i.
O
CH3O
1. LiAlH4; H3O+
2. PBr3
OCH3
CH3O
Br
(step 1)
S
1.
product(s)
of step 1
H2N
NH2
CH3O
SH
2. NaOH, H2O
(step 2)
j.
O
H
HBr
ether
HO
H
Br
k.
OH
O
O
1. PhMgBr
2. H3O+
Ph
Ph
8
Name:
l.
O
OH
250°C
(step 1)
O
product(s)
of step 1
(KSO3)2NO
H2O
(step 2)
O
m.
CH3
CH3I
S
S
I
n.
CH3
CH3
C OH
+
NaH
Br CH2
CH3
9
CH3
CH3
C O CH2
CH3
Name:
6. (10 points) Compound A (C14H20) is an optically active, aromatic compound.
Compound A undergoes ozonolysis (1. O3 2. Zn, acetic acid) to give two new
compounds B and C. Compound B (C9H10O) is optically active and contains an
aromatic ring. Compound B gives a silver mirror when treated with Tollens' reagent.
Compound C (C5H10O) is optically inactive and is unaffected by Tollens' reagent.
Compound C, when treated with LiAlH4 and then with H3O+, gives compound D
(C5H12O). Compound D, when heated with concentrated H2SO4, gives a single
compound E (C5H10). Upon ozonolysis, compound E gives equimolar amounts of
acetaldehyde and propanal. On the basis of this data, draw the structures of
compounds A to E. Ignore the possibility of geometric isomers throughout the
problem. Show your work.
A:
H CH3
*
B:
H CH3
*
CHO
C:
O
D:
OH
E:
CH3CH2CH CHCH3
10
Name:
7. (15 points) Show how you would carry out the following transformations, avoiding
product mixtures if possible. Use any organic or inorganic reagents that you need.
Show all reagents and intermediate products.
a.
OH
SCH3
OH
1. BH3
2. H2O2, NaOH
TosCl
pyridine
O
O
S
O
SCH3
CH3SNa
b.
OH
OH
O
1. NaBH4
2. H3O+
OsO4
pyridine
O
OH
CrO3
OH
OH
H2SO4
O
c.
O
HO
OH
O
PCC
(CH3)3SiCl
Et3N
O
HO
1. (CH3)2CHMgBr
2. H3O+
OSi(CH3)3
OH
11