Download Suggested Problems for Chapter 1

CHEM 2444
Answers to Practice Exam 3
Name: ______Answer Key_________________
(please print)
Please write your name above and on the back of the last page.
A worksheet is provided, but only work completed in the space available in the body of
the exam will be graded.
There are 7 questions. Read each question carefully.
1
1. (12 pts.) Circle the correct answer.
a. As with alcohols, oxidation of thiols readily occurs at the carbon attached to the
functional group.
True
or
False
b. Acid-catalyzed ring opening of epoxides does not involve nucleophilic attack at any
step.
True
or
False
c. Which compound has the lowest equilibrium constant for hydration (Khydr)?
O
O
O
CH3
H
or
or
H
d. Which compound has the most stable carbonyl group?
O
O
F3C
CF3
H3C
or
O
CH3
H3C
or
CF3
e. Which of the following could be formed by reaction of a ketone with a secondary
amine?
O
N
N
or
N
H
or
f. The Wittig reaction allows for the conversion of aldehydes and ketones to:
Imines
or
Alkenes
or
Lactones?
2
2. (20 pts.) Predict the major organic product or products expected from the
following reactions, showing stereochemistry where appropriate.
PCC
a.
OH
CH2Cl2
b.
Na2Cr2O7
OH
c.
d.
CHO
H2SO4, H2O
HI
OCH3
O
OH
O
e.
CO2H
I
ICH3
OH
NaBH4
OH
CH3OH
O
1. LiAlH4, diethyl ether
CO2H
CH2OH
2. H2O
3
f.
CH3
O
OH
CH3
NaSCH2CH3
ethanol-water
SCH2CH3
g.
CH3
O
HBr
CH3
Br
OH
HO
O
h.
CH3
NaCN, diethyl ether-water
CH3
CN
then HCl
i.
O
C6H5CCH3
j.
O
H2NC6H5
NC6H5
C6H5CCH3
O
(C6H5)3P CHCH2COCH3
O
CHCH2COCH3
4
3. (16 pts.) Propose a sequence of reactions to prepare each of the following
compounds from the indicated starting material and any necessary organic or inorganic
reagents. Note: the synthetic sequence may require you to separately prepare
intermediates for later use in the sequence.
OCH2CH3
H3C C OCH2CH3
CH2CH3
CH3CH2OH
from
CH3CH2OH
as the only source of carbon atoms
O
PCC or PDC
H3C
CH2Cl2
H
PBr3 or
SOCl2
(or HBr, HCl or HI, although slow)
O
1.
H3C
Mg
CH3CH2X
or Li
CH3CH2MgX
H OH
H
H3C
2. H3O+
or
CH2CH3
CH3CH2Li
PCC, PDC
or Na2Cr2O7, etc.
OCH2CH3
H3C C OCH2CH3
CH2CH3
O
Excess CH3CH2OH
H+
5
H3C
CH2CH3
4. (12 pts.) Draw two different routes to the following ether, ethyl propyl ether, by the
Williamson ether synthesis using any necessary organic or inorganic reagents.
CH3CH2OCH2CH2CH3
a.
CH3CH2ONa
BrCH2CH2CH3
CH3CH2OCH2CH2CH3
b.
CH3CH2Br
NaOCH2CH2CH3
CH3CH2OCH2CH2CH3
6
5. (16 pts.) The following hemiacetal can be converted to an acetal by treatment with
CH3OH in the presence of acid. Draw a detailed, stepwise mechanism for this reaction,
including all intermediates and appropriate arrows to indicate direction of electron flow.
O
OH
O
CH3OH
OCH3
HCl
O
O
H
H
OH
or
H
or
O
OCH3
O
CH3OH
H
or
O
H
H
Cl
H Cl
O
O
CH3OH
CH3OH
Okay to use either
resonance form.
O
O
CH3
H
CH3OH
or
Cl
CH3OH2
O
OCH3
or
HCl
7
6. (12 pts.) The following questions concern 13C NMR chemical shifts of epoxides and
ethers.
a. Three signals appear in the range of  55-60 in the 13C NMR spectrum of the
following compound. Circle the carbons to which these three signals correspond.
O
CH3
H3CO
b. How many signals does the following compound exhibit in its
13C
NMR spectrum?
CH3OCH(CH3)2
Number of signals: ___3___
c. Are the carbons of the analogous sulfide, CH3SCH(CH3)2, more or less shielded than
those of the above ether by 13C NMR?
More shielded
8
7. (12 pts.) An unknown compound A (molecular formula C7H14O) was treated with
NaBH4 in CH3OH to form compound B (molecular formula C7H16O). Compound A has a
strong absorption in its IR spectrum at 1716 cm-1. Compound B has strong absorption
in its IR spectrum at 3200-3600 cm-1. The 1H NMR spectra of A and B are given below.
Draw the structures of A and B.
A:
B:
OH
O
9