Br OH

Cl

Cl

Br

OH

CF3 OH

SH

NH2

CO2HCHO

Assign a configuration, R or S to each of these compounds

N+

Et

HMe

Cl

N+

Me

HMe

ClN

H

Me

Br

Problem: Compound I has two stereoisomers, but compound II and III exist as single compounds. Explain?

I II III

Problem: The following compound has only one chirality center, why then dose it have four stereoisomers

OH

OH

Me

HBr

HMe

1.

(R)

KMnO4

A (chiral) + B (achiral)

Identify A & B

2.

(R)

H2/NiC (chiral) + D (achiral)

Both C & D are C8H18, identify them.

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?

+ HBr

CO2H

CO2H CO2HHO2C

CO2H

CO2H

CO2HHO2C CO2HHO2C

Problem: Feist's acid (C6H6O4) is a cyclopropane based natural product and having twostereocenter. The compound is chiral. Based on this information predict its correct structure?

Hint:

X X

right structure

NHCO2Me

Me

OH

O

Ph

SMe SMeO

NH

O

Discuss the stereochemistry of the following compounds and mention about their optical activity with good diagrams.

Me Me Me

Me

Me Me Me

Me

Me

MeCl

Me

Me

Cl

Cl

Me

Me

Cl

Cl

Me

Me Cl

Cl

Problem: Which of the following are chiral and why?

a(p) a(p) c a(p)

ca(p) a(c) a(p)

Me Me Me

Me

Me

Me

Problem: Draw all the isomers with mol. formula C6H-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.

CO2HHO2C

CO2H

MeMe

CO2H

CO2HHO2CCO2H CO2H

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.

Hint:

heat+

heator

A

Bsame

A & B are diastereomers

Me

CH2OHEt

H

CH2OH

EtH

Me Me

Et

ClH

HOH

Et

Me

ClH

HOH

Me

Me

ClH

HOH

Me

Me

HCl

OHH

Cl Cl H Cl

Cl

Cl Cl

H H

Cl H

ClH

H Cl

Cl H

Cl H

ClH

Et Me

CH2Cl

H

Me CH2Cl

Et

H Br

BrH

H

Br

BrH

H

H

Br H Br

Indicate wheather each of the following pairs of compounds are identical or enantiomers, diastereomers or constitutional isomers.

anda. b. and

c. and d. and

ande.

f. and

g. and h. and

i.

andj. and

OH

OH

OH

OH

OHOH

OH OH

OH

OH

OHOH

OH

OH

OH

OH

OH OH

OH

OH

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.

Non resolvable (easily interconvertible by flipping)

Hint:

trans (resolvable)

cis (meso) trans (resolvable)

achiral (absence of chirality center)

Ph

Ph

BrH

HBr

H Br

HBrPh

Ph

Br

Br

HPh

PhH

Br

H

HPh

BrPh

Br

Ph

PhPh

Ph

BrH

BrH

H Br

BrHPh

Ph

Br

Br

HPh

HPh

Ph

Ph

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 Br2 to yield trans-1,2-diphenyl ethene. Suggets a mechanism?

Hnit:

Racemic

Br2 loss is not favored

meso

-HBr

-Br2

O

OH

H

H

OH

B

H

Al

H

HH

H

LiAlH4Li-sBu3BH

Problem: Reduction of 4-t-butyl cyclohexanone with LiAlH4 gives exclusively trans alcohol; whereas with lithiumtri-sec butylborohydride yields cis`alcohol exclusively? explain.

Hnit:

O OHOH

O

O

O OHOH

O

O

R

RO

R

ROH+

OHOH

R

ROH

O

OH

R

RO

+

OH

R

R

O

O+

H

O O

R R

OH

O

OHOH

O

OH

H+

A

H+

A

Hint: H+

H+

-H2O

It is more difficult to form an acetal of compound A than B?

OH

HBr

OH

HBr

Me

H

OH

Br

Me

H

OHBr

Problem: Which of these two compounds would forman epoxide on treatment with base?

A B

Hint:

A B

OO

Br

OO

OO

Br

OO

OO

Br

OO

Br

Problem: Only one of the diastereomeric bromides shown hereeliminates to give alkene A. Why? Neither bromide gives alkene B. Why not?

Base

Base

A

No alkene AAlkene B

Hint:

N CH3I N CH3+ + I

Explain the relative rate

NMeN

NMe MeN

Me

1.00 2.27 0.47 0.042

Ph

HO2C

H

HPh

HO2C

Ph

HO2C

heatheat

Explain the reaction sequences with proper explanation.

O

H

H

MgBr

O

O

a)

b) KH, 60oC

?175oC

?

Identify the missing products in the following reaction sequence.

O

O

H

H

H

H

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. 25oCHint: (ring junction cis-beta)

2.100oC light 25oC

cis-beta trans

3. 140oC 220oC

Me

Me

Me

Me

H

Me

Me

HMe

Me

H

H

Me

Me

Me

Me

MeO2C CO2Me

Problem: Account for the difference in conditions required to bring about the following transformations

176oC

400oC

Problem: Give stereochemical structures of A and B and tell exactlywhat process is taking place in each reaction

cis, cis, cis-cycloocta-1,3,5-triene100oC

A (C8H10)

A + B (C14H16O4)

Bheat

Cyclobutene + dimethylphthalate

OHO

OHPhMeCOCl OH

Ph O

O

O

CO2Me

O

Me

HO

CO2Me

Predict the products in the following reactions;

1.

KH

THF, heat?

H+

?

2.

Et3N?

LDA?

heat

H+?

Ireland-Claisen rearrangement

3. Suggest a mechanism for this reaction?

+

H

R

H

R

H

HR

R

H

HEt

MeH

H

EtMe

Each of the following transformations is believed to proceed by the indicatedsequence of concerted reactions. Show just what each step involves, and give structures of each intermediates

1. heat

Aheat

Both electrocyclic closure

2. 200oCB

260oCC

1,5-H shift, electrocyclic opening.

3. 170oC

D170oC

electrocyclic opening, electrocyclic closure

D D

D

heat

The deuterium scrambling has been accounted for on the basis ofintramolecular Diels-Alder and retro DA reactions. Show how might this occur?

Hint: look for an intermediate that is symmetrical except for the presence of deuterium.

CO2-

N2

O

?

+

?

??

Br I

Cl O Cl

Br Br

Br Br

Br Br

BrBr

Br

Br

Which alkyl halide would you expect to be more reactive in an SN2/SN1 reaction with a given nucleophile?

a.and

b. and

c. and

d. and

e. and

f. and

g. and

Me

Br

Me

Br

Me OH

Me

Br

Me Me OHMe

OH

But Br But Br

Problem: When cis-1-bromo-4-methyl cyclohexane undergoes an SN2 reaction, only trans-4-methylcyclohexanolis obtained, where as under SN1 reaction conditionboth cis and trans product is obtained. Explain

cis

OH-

SN2 OH-

cis

H2O

SN1

+

trans cis

trans

Hint:

Problem: Which of the following will react faster in an SN1 reaction?

Me Br

Me

Me

Me

Br

Br

Br

OTsBut OTs

Problem: Which of the following compounds would you expect to bemore reactive in an SN2 reaction?

A B

Hint:

A B

Ans: A

Problem: Which of the following compounds would you expect to bemore reactive in an SN2 reaction?

A B

Ans: A

NH2

OH

CHO

O

O

Br

OH CHO

O

OSO2Ar

O

OSO2Ar

Problem1 NaNO2, H2O

H2SO4

NaNO2, H2O

H2SO4

Problem 2

AgNO3

Problem 3: Kinetic measurements reveal that solvolytic displacement of sulfonateis about 5 X 105 faster for 3B than for 3A

3A3B

OO

O

I II III

Transannular participation of ether oxygen

. Unfavorable polar effect of the C-O bond

.III is more favorable than either I or II

XO

XO

X

O

X

Relative rate 1.0 0.014 0.14 4.85 x 10 4

Q.

Explain

OH

NMe2

OPh

NMe2 OH

NMe2

DEAD, TPP

PhOH

DEAD, TPP

PhOH

A B

Both A and B gave the same priduct when subjected to Mitsunobu conditions with phenol as nucleophile

OH

NO2

NO2

H

H

H

DEAD, TPP

Explain the reaction

N+M e

M e

OPh

NMe2

OH

NO2

OP+Ph3

NO2

OP+Ph3

C NO2

H

NO2

common intermediate

PhOH

TPP

DEAD

O

BrOH CHOH2O

O

BrC

+

O O

OH

OH CHOO

+

hemiacetal

Q. Describe the stereochemistry of the products of these reactions.

Cl

S

O LiAlH4

HS

O

S

S

OH_( + )

(a)

(b)

enantiomerically pure

base

Both are intramolecular SN2

RS- forms, inversion takes place (SN2) at C-atom containing Cl, forms cis-fused product

O

NH

OTs OTs

Product

KOH/H2S

Product

O

Ph

+NH

N

OH

Ph

(a)

(b)

OTs OTsKOH

H2SS

SH OTs

HS SN2

S OTsS

Q. Suggest a mechanism for the following reaction

PhN

Ph

O

O

Cl H2OPh N

H

O

O

O

Ph

CH3CN, heat

N

O

Ph

O

Ph

Cl

O

NPh

O

Ph

O

NPh

O

Ph

OH

Ph NH

O

O

O

Ph

CH2OHMeO

NH

N

I2, Ph3P

CH2OHMeO

NBS, TPP

Predict the final product

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

Me

OH

Me

OH

OH

H

OO

OH Br

OHBut But

OH

H

OH OO

OHBr