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Questions on Stereochemistry

1- Relate structures from 'b' to 'g' to structure 'a'?

H

Br

ClF

(a)

Br

H

ClF

F

Br

ClH

F

Cl

BrH

Br

H

FCl

H

F

BrCl

Cl

F

BrH

(d)

(g)(f)(e)

(c)(b)

2- Considering the Cahn, Ingold and Prelog sequence rules, put the following

groups in decreasing order of priority?

Pha) CHb) CH2

c) N

CH2Id) e)

O

H

O

CH3

O

OH

O

NH2

f)

g) CH2NH2h) i)

3- Answer true or false for each of the following statements and explain your

answer?

a) Achiral molecules cannot possess chiral centres.

b) A racemic mixture can be resolved.

c) Meso-compounds can be resolved.

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4- Designate, as 'R' or 'S', each of the following configurations?

Cl

CH3

CHH2C(a)

(d)

(g)

(f)(e)

(c)

(b)

CH3

CH3Cl

H

Br

C2H5H2C=HC

NH2

COOC2H5

COOHH

COOH

BrCl

H

CONH2

HCH3

Br H3C

Cl

H CH2Br

H

C2H5

Br

H CH3

Br

CH3H

Br

H3C CH3

Br

HH

(h)

5- Draw the Newman projection formulas for all stereoisomers and point out

their 'R or S' specifications, optical activity (where present) and meso-forms?

a) 1-Chloro-2,3-dibromobutane. b) 2,3-Diiodopentane.

6- Designate, as erythro- or threo-, each of the following compounds?

CH3

H OH

CH2CH3

H OHCH3

H OH

CH2CH3

OHH

a) b)

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7- For each of pair compounds below, determine whether the pair are

enantiomers or diastereomers?

a)

b)

OH

CH3

OH

H3C

OH

Br

OH

Br

8- a) Write the two conformations of cis-1,2-dimethylcyclohexane?

b) Would these two conformations have equal potential energy?

c) What about the two conformations of cis-1-tert-butyl-2-methyl-

cyclohexane?

9- Write the two chair conformations of each of the following and mark the

more stable conformation?

a) cis-1-tert-Butyl-3-methylcyclohexane.

b) trans-1-tert-Butyl-4-methylcyclohexane.

10-For each of the following compounds, draw both chair conformations

indicating the more stable one?

Cl

OH

CH3

OH

CH2CH3

COOH

a) b) c)

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11- Which of the following compounds has stereocentre(s)?

a) 2-Propanol b) 2-Methyl-1-butane

c) 2-Chlorobutane d) 2-Methyl-1-butanol

e) 2-Bromopentane f) 3-Methylpentane

12- Tell whether the two structures in each pair represent enantiomers or

homomers (two different orientations of the same configuration)?

H

Cl

FBr(a)

H

F

ClBr

(c)

(b)

and

H

Cl

CH3F

F

CH3

ClHand

CH3

CH2CH3

OHH

H

CH3

CH2CH3HOand

13- Draw Fisher as well as Newman projections for each of the following

compounds?

a) Erythro-2,3-dibromobutane.

b) Threo-2,3-dibromobutane.

c) Meso-2,3-dibromobutane.

14- Identify the relationship between each pair of the following compounds and

describe them as enantiomers or diastereomers?

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(a)

(b)

and

and

CH3

H Cl

CH3

H Cl

CH3

Cl H

CH3

H Cl

CH3

H Cl

CH3

H Br

CH3

Br H

CH3

Cl H

15- Draw the prespective projection of the following comounds?

a) 2-R-2-bromobutane b) 2S-3-R-2-chloro-3-bromohexane.

16- Draw the Sawhorse projections of 2S-3-R-2-chloro-3-bromobutane in each

of staggered and eclipsed conformations and mention which one is more

stable?

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