Ch 334 - Final Exam
December 6, 2000
Name (please print)
1. (12) Name the following, including stereolabels where appropriate.
CH 3
a)
CH 2
CH2
H OH
C
C
CH 3
F
CH
b)
CH2 CH2 CH2 CH3
CH3
a)
b) (name as an alkyl halide)
2. (4) The resonance method, which requires two or more Lewis structures to represent a real molecule or ion, is needed
in those cases where the valence electrons are _____________________________________________.
A single Lewis structure is unsatisfactory in these cases because it necessarily shows all valence electrons as
___________________________________________________.
3. (4) The Ka for NH4+ has been measured to be 5.5 x 10–10. Define Ka for this substance.
Ka
=
= 5.5 x 10
–1 0
4. (2) H-Cl is a stronger acid than H-F. Therefore, the Ka of H-Cl is (circle one): a) larger
b) smaller
c) the same
d) can't tell
compared to H-F.
Also the pKa of H-Cl is (circle one):
a) larger
b) smaller
c) the same
d) can't tell
compared to H-F.
5. (6) The specific three-dimensional arrangement of the four groups at a chiral center is referred to as the
___________________________________________________. The separation of a racemic mixture into the pure
enantiomers is called _________________________________________. Diastereomers are defines as
___________________________________________________________________________________.
6. (4) Rank the following in order of their reactivities as SN2 nucleophiles in the gas phase. (Assign # 1 to the most
reactive.) H2O _____
HS– _____
HO– _____
HSe– _____. Rank these same substances in order of their
reactivities as SN2 nucleophiles in polar, protic solvents. H2O _____ HS– _____ HO– _____ HSe– _____.
7. (6) A polar, protic solvent such as CH3OH can dissolve ionic compounds because both the positive and negative ions
become effectively solvated. Sketch the interactions that occur when CH3OH molecules solvate the ions shown (from
KI).
K
+
I
Π
8. (4) Refer to the reaction below.
CH3O CH2 CH2
H3C
CH3O CH2 CH2
Π
+
CH3O
CH CH2 CH2 I
H3C
+
I
Π
CH CH2 CH2 OCH3
a) if the starting material is the S enantiomer, the product will be (circle one):
R
S
can’t tell
racemic
other
b) if the starting material has (–) optical rotation, the product will necessarily be (circle one):
(+)
(–)
can’t tell
(+,–)
other
9. (8) Predict which of the four molecules below will react fastest by the mechanism indicated (circle your answer).
SN1
SN2
E1
E2
-
A
A
A
A
CH 3
CH 3 CH
B
B
B
B
C
C
C
C
CH 3
CH 2 CH
CH 3 CH 3 C
D
D
D
D
about the same
about the same
about the same
about the same
can't tell
can't tell
can't tell
can't tell
CH 3
CH 2 CH 2 CH 3 CH 3 CH
CH 3
CH 2 CH 2 CH 2 Cl
CH 3 CH
CH 2 CH 2 CH 2 I
Cl
B
A Cl
C
D
10. (4) A substitution reaction in which the solvent is the nucleophile is called ____________________________.
The compound above that would react fastest in such a reaction is ___________.
11. (12) Identify the relationship between the following pairs of molecules as one of the following:
A = identical structures
B = constitutional isomers
C = conformational isomers
D = diastereomers
E = enantiomers
F = resonance structures
G = none of these
..
HO
HO
OH
H
HO
H
H
CH3
N
CH3
O
CH3 C
Br
Br
CH3
Cl
CH3
Cl
H
CH3 Cl
H
CH2CH3
Cl
H
CH3
CH3CH2
Cl
CH3
N
CH3
N
H
H
CH3
H
Br
Br
Br
H
H
CH3
..
CH3 C
H
CH3
N
O
H
Cl
H
CH3
Br
12. (6) Use Fischer projections to show all of the stereoisomers of CH 3-CHOH-CH2-CHOH-CH3. Indicate pairs of
enantiomers and pairs of diastereomers.
13. (42) Complete the following reactions by showing products, reactants or reagents, as appropriate. Indicate
stereochemistry clearly for those marked with a star ().
H3C
Br
t-Bu-O
a)
Π
+
t-Bu-OH
major
CH3
D
CH 2 CH 3
+
b)
H
minor
h
Br2
H
H
c)
H3C
H
H
CH3
+
HI
SN
OH
CH3
d) CH3-S-CH3
+
F
CH3 H
H
S
CH3
Br
CH3
e) CH3O
+
H
H
NaNH2
OH
H3C
Cl
H
H
H3C
C
H
H
f)
O
CH3
g) H
OH
CH2
CH3
CH 3
S
O
Cl
Li-Br
N
14. (20) Write mechanisms for the following. Show individual steps clearly, include any formal charges, and
use correct electron pushing. The use of the symbol H+ is unacceptable.
Br
h
Br2
+
+ H-Br
a)
CH3
b)
CH3 CH
4
H3C
3
2
1
CH CH2 CH2 OH
OH
H2SO4
4
CH3
C CH 3
2
O
CH2
1
+ H2O
CH2
2
15. (14) a) Complete and balance the following, assuming an elimination reaction:
CH3
I
+
+ –
K
O-C(CH3 )3
b) This elimination probably occurs with an
mechanism.
form
elimination is usually
The
rate
law
would
have
the
. The stereochemistry for this type of
.
c) For the cis isomer of the above iodide, there are two possible chair conformations, but only one reacts rapidly
in the elimination reaction. Carefully draw the structure of this chair conformation, and write the mechanism for
elimination. Show individual steps clearly, and use correct electron pushing.