The racemic dibromide undergoes an E2 elimination with pyridine as the base to give the trans product selectively. This is because the anti-periplanar conformation required for E2 is favored for one enantiomer due to less steric interaction between the phenyl groups. The meso dibromide cannot undergo such a stereospecific E2 reaction. Instead, it undergoes a thermally allowed homolytic cleavage of the weaker C-Br bond to eliminate Br2. This reaction does not require a particular transition state geometry.

1. Assign a configuration, R or S to each of these compounds
Br
Cl
Cl
OH HO
Br
CF3 OH
NH2
HS CHO
CO2H

2. Problem: Compound I has two stereoisomers, but compound
II and III exist as single compounds. Explain?
+ +
Me N H Me N H Me N
Et Cl Me Cl H
I II III
Problem: The following compound has only one chirality center,
why then dose it have four stereoisomers
Br

3. 1.
KMnO4
HO
A (chiral) + B (achiral)
OH
(R) Identify A & B
2.
H2/Ni
C (chiral) + D (achiral)
Both C & D are C8H18, identify them.
(R)
3. Two stereoisomers are obtained from the reaction of HBr with (3S, 4S)-4-bromo-3-methyl-1-pentene.
one of the stereoisomer is optically active and the other is not. Explain?
Me H
+ HBr
Br H
Me

4. Problem: Feist's acid (C6H6O4) is a cyclopropane based natural product and having two
stereocenter. The compound is chiral. Based on this information predict its correct structure?
CO2H CO2H
Hint:
CO2H HO2C CO2H CO2H
X X
HO2C CO2H HO2C CO2H
right structure

5. Discuss the stereochemistry of the following compounds and
mention about their optical activity with good diagrams.
OH
NHCO2Me
O
Ph
Me
O
SMe O SMe
N
H

6. Problem: Which of the following are chiral and why?
Me
Me
Me Me Me Me Me
a(p) Me
a(p) c a(p)
Me Cl Me
Me Cl Me
Cl Cl
Cl Me Cl
Me Me Cl Me
c
a(p) a(c) a(p)

7. Problem: Draw all the isomers with mol. formula C 6H-12 that
contain a cyclobutane ring, and comment on their chirality
Hint: the base structure is dimethyl cyclobutane [1,2 (cis & trans) and
1,3 (cis & trans) also 1,1]; there also exist 1ethyl cyclobutane.
Me Me Me Me
Me
Me

8. Problem: 2,5-dimethyl-1,1-cyclopentane dicarboxylic acid exist as two optically
inactive isomers (A & B; differ in mp),Upon heating (mono decarboxylation A yields
two 2,5-dimethylcyclopentanecarboxylic acid and B yields one.
Assign structures of A & B.
HO2C CO2H
Hint:
CO2H CO2H
heat
A + Me Me
CO2H CO2H
HO2C CO2H
heat
or
B
same
A & B are diastereomers

9. Indicate wheather each of the following pairs of compounds
are identical or enantiomers, diastereomers or constitutional isomers.
H Me Me Et
a. Et CH2OH and H Et b. HO H HO H
Me CH2OH and
H Cl H Cl
Et Me
Me Me
HO H H OH
c. and d. and Cl
H Cl Cl H
Me Me
Cl Cl H Cl
e. H H H Cl Cl H H Cl
and f. and
Cl Cl Cl H H Cl Cl H
Br H
CH2Cl Et H Br
g. h. and
Et Me and Me CH2Cl
H Br
H H Br H
i. H
j. and
and Br H Br

10. Problem: Which of the following compounds are resolvable,
and which are non resolvable?Which are truly meso?
a) cis-1,2-cyclohexane diol; b) trans-1,2-cyclohexane diol;
c) cis-1,3-cyclohexane diol; d) trans-1,3-cyclohexane diol;
e) cis-1,4-cyclohexane diol; f) trans-1,4-cyclohexane diol.
Hint:
OH
OH
OH
OH OH
OH
OH
OH trans (resolvable)
Non resolvable (easily interconvertible by flipping)
OH
OH OH
HO
OH OH
cis (meso) trans (resolvable)
OH
OH
HO OH
HO
OH
achiral (absence of chirality center)

11. Problem: On treatment with the aromatic base pyridine, racemic 1,2-dibromo-1,2-diphenyl ethane
loses HBr to yield trans-1-bromo-1,2-diphenyl ethane; In contrast the meso dibromide loses Br 2 to
yield trans-1,2-diphenyl ethene. Suggets a mechanism?
Hnit: Ph Br
Ph
Br
Ph H
Br H H H Ph Br2 loss is not favored
Ph
H Br H Br
Br
Ph
Racemic
H
Ph -HBr Ph
H Br
Ph
Br Ph
Ph Ph Br Br
PhH Ph
H Br Ph
Br H H -Br2
H Br Ph Ph
H Br
Ph Br
meso

12. Problem: Reduction of 4-t-butyl cyclohexanone with LiAlH 4 gives exclusively
trans alcohol; whereas with lithiumtri-sec butylborohydride yields cis`alcohol
exclusively? explain.
Hnit:
OH H
Li-sBu3BH O LiAlH4
H OH
H
Al
H H
B H
H

13. It is more difficult to form an acetal of compound A than B?
O
OH
O HO
O
H+
A
O
OH
O HO
O
H+
A
R R R R +
Hint: H+ O
O OH+ OH
R H+ R R O -H2O R OH
OH
HO OH
R R
O O R O
+
O
R
H
HO
OH HO
OH
O O

14. Problem: Which of these two compounds would form
an epoxide on treatment with base?
OH OH
Br Br
H H
A B
Hint: Me OH Me
OH
Br
H Br H
A B

15. Problem: Only one of the diastereomeric bromides shown here
eliminates to give alkene A. Why? Neither bromide gives alkene B. Why not?
O O
O O
Base
O
Br O
A
O
O
Base Alkene B
No alkene A
Br
Hint: O O
O O
Br
Br

16. N + CH3I N CH3 + I
Explain the relative rate
Me
N Me N Me
N Me
N
2.27 0.47 0.042
1.00

17. Explain the reaction sequences with proper explanation.
H
Ph
heat Ph H
heat Ph
HO2C
HO2C
HO2C

18. Identify the missing products in the following reaction sequence.
O a) MgBr
175oC
? ?
H
b) KH, 60oC O
H
O

19. Each of the following reactions involves one or more concerted steps
that take place in accordance with theWoodward-Hoffmann rules. In each case,
prdeict exactly what is happening, with stereochemistry?
1. 25oC
O Hint: (ring junction cis-beta)
O
100oC light 25oC
2.
cis-beta trans
H H
140oC 220oC
3.
H H

20. Problem: Account for the difference in conditions required
to bring about the following transformations
Me
Me Me Me
176oC H
Me
Me Me Me
H
Me H Me
400oC
Me Me
H
Problem: Give stereochemical structures of A and B and tell exactly
what process is taking place in each reaction
100oC
cis, cis, cis-cycloocta-1,3,5-triene A (C8H10)
A+ MeO2C CO2Me B (C14H16O4)
heat
B Cyclobutene + dimethylphthalate

21. Predict the products in the following reactions;
O
1. OH
KH H+
? ?
THF, heat
2. MeCOCl LDA heat OH
Ph OH ? ? ?
Et3N H+
Ph O
Ireland-Claisen rearrangement
3. Suggest a mechanism for this reaction?
Me
O
+
O O O
H
CO2Me CO2Me

22. Each of the following transformations is believed to proceed by the indicated
sequence of concerted reactions. Show just what each step involves,
and give structures of each intermediates
1. H
H R
heat heat
R A
R
R
H H
Both electrocyclic closure
2. 200oC 260oC
B C
1,5-H shift, electrocyclic opening.
Me
H H Et
Me 170oC 170oC
3. D
Et
H
H
electrocyclic opening, electrocyclic closure

23. The deuterium scrambling has been accounted for on the basis ofintramolecular
Diels-Alder and retro DA reactions. Show how might this occur?
heat
D D
D
Hint: look for an intermediate that is symmetrical except for the presence of deuterium.

24. ?
+
N2
? ?
CO2-
O
?

25. Which alkyl halide would you expect to be more reactive
in an SN2/SN1 reaction with a given nucleophile?
a.
Br and I
e. Br Br
b. Cl and
and O Cl
f. and Br
c. Br Br Br
and
g. Br
and
d. and Br
Br Br

26. Problem: When cis-1-bromo-4-methyl cyclohexane undergoes an SN2 reaction,
only trans-4-methylcyclohexanolis obtained, where as under SN1 reaction condition
both cis and trans product is obtained. Explain
Hint:
Br Br
Me OH- Me Me OH
SN2 OH- trans
cis
Br OH
H 2O +
Me Me Me OH Me
SN1
cis trans cis
Problem: Which of the following will react faster in an SN1 reaction?
But Br But Br

27. Problem: Which of the following compounds would you expect to be
more reactive in an SN2 reaction?
Br
Br Hint: Br
Me Me
Me Br Me A B
A B
Ans: A
Problem: Which of the following compounds would you expect to be
more reactive in an SN2 reaction?
But OTs OTs Ans: A
A B

28. NH2 NaNO2, H2O CHO
Problem1
OH
H2SO4
NaNO2, H2O
O
H2SO4
Problem 2
O
AgNO3 HO CHO
Br
Problem 3: Kinetic measurements reveal that solvolytic displacement of sulfonate
is about 5 X 105 faster for 3B than for 3A
OSO2Ar
OSO2Ar
O O
3A
3B

29. Q.
O
X X X X
O
O
Relative rate 1.0 0.014 0.14 4.85 x 10 4
Explain
Transannular participation of ether oxygen
O
O O
.
I II III
. III is more favorable than either I or II
Unfavorable polar effect of the C-O bond

30. OH OPh NMe2
DEAD, TPP DEAD, TPP
NMe2 NMe2 OH
PhOH PhOH
A B
Both A and B gave the same priduct when subjected to Mitsunobu conditions with phenol as nucleophile
H
H
OH DEAD, TPP
NO2
NO2
H
Explain the reaction

31. PhOH
Me OPh
+
N
Me NMe2
common intermediate
OH OP+Ph3 OP+Ph3
TPP NO2
DEAD NO2
NO2 C NO2
H

32. O
H2O HO CHO
Br

33. O O O
Br +
hemiacetal
C
HO
+
O
HO CHO

34. Q. Describe the stereochemistry of the products of these reactions.
Cl
O LiAlH4 S
(a)
S
(_)
+
-
forms, inversion takes place (SN2) at C-atom containing Cl, forms cis-fused product
OH
O S
base
(b) HS
enantiomerically pure
Both are intramolecular SN2

35. H
N
O
Product
OTs OTs KOH/H2S
Product

36. OH
O
(a) + N
Ph N Ph
H
OTs OTs
KOH
(b)
H2S
S
HS SN 2
SH OTs S
S OTs

37. Q. Suggest a mechanism for the following reaction
O O
H2O O Ph
Ph Cl
N Ph N
CH3CN, heat H
Ph O
O
O O
O
Cl
Ph N Ph N
Ph N
O O Ph O
Ph Ph
OH
O
O Ph
Ph N
H
O

38. Predict the final product
I2, Ph3P
MeO CH2OH
N
N
H
NBS, TPP
MeO CH2OH

39. For each of the compounds A through H indicate the number of gauche butane
interactions present in the most stable chair conformation.

40. Me Me
OH OH HO Br
OH O
O
H

41. But But
OH HO
Br
OH
OH O O
H