CHEM 334. Problem Set 1 Spring 2014 Prof Donald Watson 1
2
1. Allyl Bromides are excellent electrophile in SN and SN reaction. By considering both
competitive reaction pathways explain it on the basis of FMO analysis.
2. Draw the important resonance contributors for the following cations, anions and radicals.
CH2
O
a H2C
O
H
b.
H
c.
d.
H
H
COMe
O
f
e
O
g
OMe
CH2
h H C
2
CH2
Me
Me
O
3. Construct the MOs for pentadienyl cation and identify Frontier Molecular Orbitals.
CH2
4. Identify A and B from the following sequence of reactions.
O
Me
O
CO2Me
150 °C
O
-CO2
Dield-Alder
Product
24 h
Final Product
B
A
5. Propose a synthesis of the following compounds.
H
O
O
Me
a.
O
b.
H
O
O
Me
c.
O
H
CN
CN
H
Me
d.
S
O
CN
H
H
CN
6. Furan and Maleimide undergo a Diels-Alder reaction at 25 °C to give the endo isomer of the
product. When the reaction takes place at 90 °C, however, the major product is the exo
isomer. Further study shows that the endo isomer of the product isomerizes to the exo
isomer at 90 °C.
O
O
Furan
NH
O
Maleimide
a. Draw and label the endo and exo isomers of the Diel-Alder adduct of the furan and
maleimide.
b. Which isomer of the product would you usually expected from this reaction? Explain why
this isomer is usually favoured.
c. Examine your answer to (b) and determine whether this answer applies to a reaction that
is kinetically controlled or thermodynamically controlled or both.
d. Explain why the endo isomer predominates when the reaction takes place at 25 °C and
why the exo isomer predominates at 90 °C.
7. Suggest suitable reagents for carrying out each step in the following synthetic sequence.
O
a
Br
Br
b
O
c
d
O
O
Br
Br
O
O
8. Give the product of ring-closing metathesis for each of the following reaction.
b.
a.
9. Identify the product of Heck reaction for each of the following reaction.
a. Me
I
CN
Me
O
b. Me
Me
Br
PdL2
Et3N
PdL2
Et3N
10. Give the product formed when following compound undergoes electrocyclic reaction. Show
how FMO ( Draw HOMO and LUMO) analysis helps in predicting the stereochemical
outcome of the product.
Δ
Me
Me
hν
11. Draw arrow-pushing mechanism and FMO (HOMO and LUMO) diagram for the following
synthetic transformation.
Et2NH
Me
Me
Cl
NEt2
12. “The Nucleophiles attack only at terminal of the π-allyl species”. How does the MOs of the
Allyl cation would be modified to substantiate the above statement. Clue: Look at ψ2, ψ3 and
resonance diagram
CH2
Energy
ψ3
ψ2
ψ1
CH2
H2C