Question 1. (15 points) Label each of the following compounds as aromatic,
antiaromatic or nonaromatic. Give a brief explanation for your answer.
Answer____________________________
nonaromatic
Explanation:
a)
No continuous planar cyclic π-system = nonaromatic
N
antiaromatic
Answer____________________________
H
N
b)
Explanation:
4 e- cyclic planar π-system (nitrogen contributes 2 e-) = antiaromatic
aromatic
Answer____________________________
c)
Explanation:
6 e- cyclic planar π-system= aromatic
Question 2. (6 points) Circle the compound that corresponds to the pictured 13C NMR
spectrum.
O
a)
OH
b)
OH
c)
d)
CH3
Question 3. (15 points) For each compound below, identify whether the circled hydrogen
atoms are homotopic, enantiotopic, or diastereotopic.
H
a)
Your answer:
H
CH3
H3C
diastereotopic
Cl
Your answer:
H
H
b)
enantiotopic
CH3
H3C
Your answer:
H
homotopic
c)
H
Question 4. (18 points) For each of the compounds below, identify the approximate
chemical shift and multiplicity for the circled hydrogen atom(s) that will appear in the
corresponding 1H NMR spectrum.
Chemical Shift: _____5.5 ppm_______________
a)
Multiplicity:
H
H3C
CH3
b)
_triplet (triplet of triplets is OK)_
Chemical Shift: ______1.5 ppm______________
CH2
Multiplicity:
______triplet________________
O
CH3
H
Chemical Shift: ______7.3 ppm_____________
c)
Multiplicity:
Cl
Cl
______doublet______________
Question 5. (20 points) Clearly draw all the π molecular orbitals for compound A (shown
below), and include orbital phases (a “top view” is OK). Make sure to:
a)
b)
c)
d)
Identify all nodes with dotted lines
Indicate how many electrons occupy each orbital
Label the HOMO
Label the LUMO
A
(4 nodes)
Ψ5
(3 nodes)
Ψ4
(2 nodes)
LUMO
Ψ3
(1 node)
HOMO
Ψ2
(0 nodes)
Ψ1
Question 6. (10 points) In the space provided, identify the reactants that will produce
compound B via a Diels-Alder reaction
H3C
H3C
heat
+
H3C
CH3
H
H
H3C
H3C
O
B
O
Question 7. (6 points) The mass spectrum for 3-buten-2-ol is shown below.
57
CH3
OH
parent ion
In the space below, draw the structure of the fragment ion that most likely corresponds to
the base peak in the above mass spectrum, and provide a clear explanation for your
answer.
OH
OH
OH
β-cleavage of the methyl group yield a highly resonance stabilized fragment
Question 8. (10 points) Identify which of the pictured compounds corresponds to the IR
spectra shown below.
CH3
OH
H3C
A
O
H
H3C
H3C
B
H
C
CH3
H3C
O
O
OH
D
H3C
CH3
H3C
E
a)
The above spectrum corresponds to compound ____B________
b)
The above spectrum corresponds to compound ____C_________
CH2
F
Extra Credit (5 points). Identify the product (including stereochemistry) of the reaction
shown below. This question is hard – finish the rest of the test first!
CN
H
heat
CN
H
H
H
NC
H
H
H
Diels-Alder reaction, endo transition state
NC
H