Questions on Stereochemistry 1- Relate structures from 'b' to 'g' to structure 'a'? H
Br
F
Cl
F
F
F Cl
H
H
Cl
Br
Br
H
Br
Cl
(a)
(b)
(c)
(d)
H
Br Cl
Cl
Cl
F
Br
H
Br
H
F
F
(e)
(f)
(g)
2- Considering the Cahn, Ingold and Prelog sequence rules, put the following groups in decreasing order of priority? a)
Ph
b)
CH
c)
CH2
O
O
d)
CH2I
f)
e)
OH
H
O
O
g)
CH2NH2
N
i)
h)
CH3
NH2
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. 1
4- Designate, as 'R' or 'S', each of the following configurations? Cl
(a)
H2C
H
CH3
(b)
CH
Cl
CH3
H2C=HC
CH3
Br
NH2
(c)
H
C2H5
COOH
(d)
COOH
H Cl
Br COOC2H5
H Cl
CONH2
C2H5
(e)
(f)
Br CH3
H
H3C H CH2Br Br
Br H
H3C
CH3
(g) H
CH3
(h) H
CH3
H Br
Br
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
H
OH
a)
H
CH2CH3 OH
b) H
OH CH3
CH2CH3
2
7- For each of pair compounds below, determine whether the pair are enantiomers or diastereomers? OH
OH
CH3
a)
H3C
OH
OH
b)
Br
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-methylcyclohexane?
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
COOH
CH3
a)
c)
b)
OH
OH CH2CH3
3
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
H
(a) Br
(b)
(c)
F
and
Br
Cl
Cl
F
H
F
F
CH3
and
H
Cl
Cl
CH3
CH3
H
H
OH
and
HO
CH2CH3 CH3
CH2CH3
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?
4
CH3 H
CH3 Cl
(a)
Cl
H
H
Cl
and H
Cl CH3
CH3
CH3
CH3
H
Cl
(b)
Br
H
Cl
H
and H
Br CH3
CH3
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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