Chem 331; 2002 Exam 1 (10/4/02) answers
1. Give the hybridization for each non-H atom (10 points)
O sp
sp 3
sp
H2 N
2
sp 2
sp 3
sp
sp 3
2.
Draw the structure (16 points each)
2a. (1R)-2,2-diethylcyclohexanecarboxaldehyde
CHO
b. (2S, 4Z)-2-methyl-4-heptenenitrile
16 pts
OHC
CN
C
16 pts
N
16 pts
3. Give IUPAC names for each molecule (16 points each)
a.
O
HO
OH
4-hydroxybutanoic acid
SH
b.
(2R,3S)-3-bromo-2-butanethiol
H
CH3
H3C
Br
H
O
c.
(2R)-2-bromopropyl (2E,4R)-4-amino-2-pentenoate
O
NH2
Br
Chem 331; 2002 Exam 1 (10/4/02) answers
4. (20 points each) For each pair of cyclohexanes, which is more stable. Explain your
reasoning in detail (no credit for a correct guess, only a correct explanation)
a
Etequatorial
tBu
tBu
Et
H
A
tBu
H
Etaxial
H
B
more stable
H
tBu
Et
For both A and B, the favored conformation has the t-Bu groups in the equatorial positions. This places the Et
group of A in the equatorial position, and the Et group of B in the axial position.
b
Braxial
Meaxial
Me
Br
H
A
Me
Brequatorial
tBu
tBu
Br
Meequatorial
tBu
H
tBu
B
more stable
For both A and B, the favored conformation has the t-Bu groups in the equatorial positions. A has an axial methyl
group, which 'costs' 1.70 kcal (Table 4-3 on pg 142 in V&S). B has an axial bromine, which costs 0.55 kcal/mol. B
is more stable.
6. The 'bridgehead' alkene 1 is extremely unstable. Use a clear orbital picture and less
than 15 words to explain why. Hint: the answer has to do with the π-bond.
1
side view
The σ framework holds the p orbitals at a ~90 °. They cannot overlap and therefore
cannot bond.
NAME
5. Provide a detailed arrow pushing mechanism for the following reaction
Br
Bu3 SnH
H
AIBN
O
H
H
O
Initiation
NC
N N
CN
AIBN
Br
:N N: +
• CN
H SnBu3
H-atom
extraction
• SnBu3
•
Br-atom
extraction
O
•
O
multiple
bond
addition
H
O
Bu3Sn•
H
H
Bu3Sn
H
H
•
O
+
• SnBu3
H-atom
extraction
O
H
H
H
multiple
bond
addition
NAME
6. The 'bridgehead' alkene 1 is extremely unstable. Use a clear orbital picture and less
than 15 words to explain why. Hint: the answer has to do with the π-bond.
1
side view
The σ framework holds the p orbitals at a ~90 °. They cannot overlap and therefore
cannot bond.