(CHE 325) Organic Chemistry II Spring 2011 EXAM #3 Name: KEY ID#: Check your exam to be sure it is complete. There are seven questions in this exam. It is worth 100 points. To receive full credit for your submissions, make sure you do your own work. Read each question carefully, and answer in clearly legible and coherent English. Use the back of the page for additional space if needed. 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. Good luck! N. Totah 1. (of 11) 2. (of 8) 3. (of 10) 4. (of 8) 5. (of 38) 6. (of 10) 7. (of 15) Total: (100)
Transcript
(CHE 325) Organic Chemistry II Spring 2011
EXAM #3
Name: KEY ID#: Check your exam to be sure it is complete. There are seven questions in this exam. It is worth 100 points. To receive full credit for your submissions, make sure you do your own work. Read each question carefully, and answer in clearly legible and coherent English. Use the back of the page for additional space if needed. 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. Good luck!
1. (11 points) Give IUPAC names for the following compounds: a. CCl N 4-chlorobutanenitri le b.
O
OCH2CH3
ethyl benzoate c.
O
O O
pentanoic anhydride d.
O
OH
OH 2-hydroxyheptanoic acid e.
N
O
CH3
CH3
H N,N-dimethylprop-2-ynamide
Name:
3
2a. (4 points) Rank the following compounds in order of decreasing acidity. Rank the most acidic compound 1, and the least acidic compound 4. Place the number corresponding to the relative acidity of each compound in the blank below it.
1 243
CO2HMe3NOH
CH3 CO2HCO2H
OMe
OMe
2b. (4 points) Rank the following compounds in order of decreasing reactivity to nucleophilic acyl substitution. Rank the most reactive compound 1, and the least reactive compound 4. Place the number corresponding to the relative reactivity of each compound in the blank below it.
431 2
OCH3
O
OCH3
O
NHCH3
O
O
O O
Name:
4
3. Write a complete, stepwise mechanism to account for each of the following transformations. Use curved arrows to denote electron flow. a. (3 points)
R OCH3
O
R SCH3
O
+ NaOCH3
NaSCH3
mechanism:
R O
O
CH3 RO
O
CH3SCH3
SCH3
R SCH3
O
+ OCH3
b. (7 points)
OHO
O
H OCH3
CH3OH
H+ catalyst+ H2O
H
mechanism:
O
HO
O
H
OCH3
HO
O
H
H
O OH
H
O OH
H
O
proton
transfer
O OCH3
H
H
H
H HH - H+
H+
HOCH3
- H2O
Name:
5
4. (8 points) Clearly explain how you could distinguish between each set of compounds using the spectral technique indicated. For full credit, identify what distinguishing features you would expect to see for each compound. Be specific. Cite numerical values/ranges and identify relevant functional groups to support your claims. a. Distinguish between A and B using 13C NMR spectroscopy
NH2
O
H
O
A B
vs.
The compounds can be distinguished easily be the chemical shift of the carbonyl carbon atom in each functional group:
A: the amide wil l have a shift between δ 160 - 180
B: the aldehyde wil l have a shift between δ 190 - 220
b. Distinguish between C and D using Mass Spectrometry
O
vs.O
C D
D: wil l show a fragment due to a McLafferty rearrangment so wil l see a peak at m/z = 58; or wil l see a loss of 28amu
OH
(CH2=CH2) C: wil l not
Note: Both C and D wil l show the same alpha cleavage products so these fragments don't distinguish the two
Name:
6
5. (38 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.
OH
O
1. NaH
2.
Cl
OO
O O
b.
(step 1)
OH
CrO3
H2SO4 OH
O
product(s) of step 1
(step 2)
1. NaH
2. BrO
O
c.
O
H
Ph3P CHCH2CH3
H
H
Name:
7
d.
CO2H
SOCl2
O Cl
e.
CH3O OCH3
H3O+
O
f.
N 1. LiAlH4
2. H2O
O
N
g.
(step 1)
H
O
KCN
HCNCN
OH
OH
O
H1. DIBAH
2. H2O
product(s) of step 1
(step 2)
Name:
8
h.
HO
OH Cl
O
(1 equiv)
Et3N
O
OHO
i.
(step 1)
O
(CH3CH2)2CuLi
O
H2NNH2
KOH
product(s) of step 1
(step 2) j.
NH2
O
SOCl2 CN
k.
O OPh1. LiAlH4
2. H3O+ PhOH
OH
Name:
9
l.
ONH
pH = 4.5
N
m.
(step 1)
H3O+
heatH2N
O
HO
O
CH3CH2OH
HCl (cat)
product(s) of step 1
(step 2)
CH3CH2O
O
n.
CH3O
OH
O
O
CH3OOH
O
1. BH3
2. H3O+
o.
OO ONH2
NHO
O
OH
Name:
10
6. (10 points) A neutral compound A (C7H14O) has the 1H NMR spectrum shown on the following page. Compound A reacts with 2,4-dinitrophenylhydrazine to give a positive 2,4-DNP test. Compound A also reacts with phenylmagnesium bromide (1. PhMgBr, 2. H3O+) to give a new compound B (C13H20O). Upon treatment with concentrated HBr Compound B reacts to give compound C (C13H19Br). Compound C is carried through a sequence of reactions (1. Mg°, 2. CO2, 3. H3O+) to give a final product D that shows two strong absorptions (3200 [broad], 1710 cm-1) in the IR. Identify the lettered compounds A - D by drawing structural formulas for each. Show your reasoning, including a complete interpretation of the NMR data provided for compound A (e.g. show how every resonance in the NMR corresponds to the structure you propose for compound A; label each peak).
O
HO
Br
HO2C
A
B
C
D
positive 2,4-DNP test says A is an aldehyde or ketone IR data indicates that compound D is a carboxylic acid C=O 1710 cm-1 OH 3200 cm-1
1H NMR assignments for A are shown on the following page
Name:
11
1H NMR spectrum for Compound A: (integral values are provided above each resonance)
6H
3H
2H
2H
1H
a
e
db
c
Compound A:
O
a b
c
d
e
a
Name:
12
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.
