Answer Key
Name:_____________________________
GT Student ID:_____________________________
CHEM 2312: Assignment 2
Due on Friday, August 29, 2025, at 10 pm. Please write your answers within the given space. Do not
submit any separate sheets.
1. (5 points) Which of the following cations are stabilized by resonance?
O
NH 2
H 2N
Cl
NH 2
E
a. I, II, III, IV
N
H
I
HN
II
b. II, IV, V
N
H
H
III
IV
V
c. II, IV
d. III, V
e. I, II, IV
2. (5 points) According to the molecular orbital model of the cyclopentadienyl anion, how many pelectrons are in anti-bonding molecular orbitals?
A
a. 0
b. 1
c. 2
d. 3
e. 4
3. (5 points) On the basis of molecular orbital theory and Hückel’s rule, which of the following should be
aromatic?
H
N
I
II
III
N
H
O
IV
V
N
VI
D
a. II, V, VI, IX, X
d. I, II, V, VIII, X
VII
VIII
b. III, IV, VI, VII
e. I, V, VIII
IX
H
H
X
c. II, IV, V, VIII, X
4. (5 points) A correct IUPAC name of the compound below is:
a. (2E,4Z,6E)-2,4,6-Nonatriene
c. (2E,4Z,6Z)-2,4,6-Nonatriene
e. (3Z,5E,7E)-3,5,7-Nonatriene
B
b. (2Z,4Z,6E)-2,4,6-Nonatriene
d. (3Z,5Z,7E)-3,5,7-Nonatriene
5. (5 points) Select the structure(s) containing a conjugated diene:
C
I
C
II
a. I and II
III
b. III, IV, and V
IV
c. III and IV
V
d. V
e. I, II, and V
6. (5 points) Arrange the following dienes in the order of decreasing stability:
I
C
II
a. II > IV > III > I
d. I > III > IV > II
III
IV
b. IV > II > III > I
e. III > I > II > IV
c. IV > II > I > III
7. (5 points) The diagram below, which describes the fate of intermediate K in a reversible reaction to
yield P1 and P2, implies:
Intermediate K has a short lifetime.
The more stable product forms more rapidly.
The less stable product forms more rapidly.
Product P2 will predominate at equilibrium.
Both, c and d are correct.
potential energy
E
a.
b.
c.
d.
e.
K
P1
P2
reaction coordinate
8. (5 points) Which alkene would you expect to have the lowest heat of hydrogenation (= least
exothermic)?
C
a.
b.
c.
d.
e.
9. (5 points) Which of the following compound would you expect to have the shortest C-C single bond?
A
a.
b.
c.
d.
e.
10. (5 points) Which of the following compounds would you expect to have the lowest-energy UV-vis
absorption?
A
a.
b.
c.
d.
e.
11. (5 points) Which of these conjugated dienes cannot undergo a Diels-Alder reaction?
B
a.
b.
c.
d.
e.
12. (5 points) Which diene and dienophile would you choose to synthesize compound Q?
Q
CN
CN
CN
CN
a.
and
b.
and
CN
CN
C
c.
and
NC
e.
and
NC
CN
d.
and
CN
CN
CN
13. (15 points) State the hybridization of the atom in bold script for each of the following structures:
OAc
I
a.
N
O
sp2
b.
dsp3
OAc
c.
C
sp2
14. Consider the following acid-base equilibria:
H
N
N
pyridine
H
N
pyrrole
pK a = 5.25
+ H
H
N
+ H
H
H
pK a = 0.4
a) (5 points) Provide a rationale for the very weak basicity of pyrrole, which is almost 100,000-times
lower compared to pyridine.
The lone pair of the pyrrole nitrogen participates in the delocalized aromatic pi-system. Upon
protonation, the lone pair is no longer available to participate in the resonance stabiliation of the
ring electrons, resulting in an overall non-aromatic structure associatedf with a large loss in
resonance stabilization energy. In contrast, the pyridine lone pair does not participate in
resonance stabilization and is oriented perpendicular to the ring pi-system. Thus, protonation has
not significant effect on the aromaticity of the pyridine ring.
Note: Pyridine is much less basic compared to aliphatic amines such as triethyl amine. The lower
basicity of pyridine is due to the increased s-character of the pyridine nitrogen lone pair, rendering
the nitrogen more electronegative and therefore less basic.
b) (5 points) Briefly explain why pyrrole is preferentially protonated on the ring carbon in the 2-position
rather than the nitrogen whereas for pyridine the opposite is observed.
Protonation of the ring carbon in pyrrole produces a resonance-stabilized carbocation whereas
protonation of the pyrrole nitrogen would result in a non-resonance stabilized non-aromatic cation.
In contrast, protonation of the pyridine lone pair has no significant effect on the delocalized
aromatic pyridine ring whereas protonation of the ring-carbon would disrupt aromaticity.
15. (15 points) For each of the following reactions, fill in the missing starting material, reagent, or
product(s).
a)
Br
HBr
+
Br
b)
O
O
O
140 °C
O
c)
NBS
ROOR
H
O
H
O