Chemistry 2500 A - Fall 2001
1.
Answers to Additional Questions on Assignment #4
In question #1 of Assignment #1, you were asked to draw every thiol with the molecular formula C6H14S (see the answer
guide on the web page to be sure you have them all.) Which of these can exist as stereoisomers? Write out perspective
structures for each possible stereoisomer, assigning each stereogenic carbon atom as (R) or (S). Hint: consider
abbreviating hydrocarbon groups attached to the chiral carbon atom as Me, Et, n,iPr, n,s,tBu, etc., to save space and time
in your drawings.
The formulas which have one (or more) stereogenic carbon center are circled below:
Molecular Formula =C6H14S
Parent HC (# of unique H types)
hexane (3)
2-methylpentane (5) 3-methylpentane (4) 2,3-dimethylbutane (2) 2,2-dimethylbutane (3)
Derivatives of hexane
2°
2°
2°
1°
1°
SH
1°
2°
2°
1°
2°
1-hexanethiol
1°
SH
2°
SH
2°
2°
1°
2°
2-hexanethiol
2°
2°
3-hexanethiol
Derivatives of 2-methylpentane
1°
1°
3°
2°
1°
1°
2°
SH
1°
1°
2°
2-methyl-1-pentanethiol
2°
SH
1°
3°
2°
1°
3°
2°
1°
2°
1°
2°
4-methyl-2-pentanethiol
OR 2-methyl-4-pentanethiol
3°
HS
1°
2-methyl-3-pentanethiol
1°
2°
3°
1°
SH
2-methyl-2-pentanethiol
1°
SH
1°
2°
4-methyl-1-pentanethiol
Derivatives of 3-methylpentane
2°
1°
SH
2°
1°
1°
2°
3°
1°
1°
2°
SH
2°
3°
1°
SH
3°
1°
1°
3-methyl-2-pentanethiol
3-methyl-3-pentanethiol
1°
1°
1°
3°
3°
3°
SH
1°
1°
SH
3°
1°
1°
2,3-dimethyl-1-butanethiol
2,3-dimethyl-2-butanethiol
Derivatives of 2,2-dimethylbutane
1°
1°
1°
4°
1°
SH
1°
1°
1°
4°
2°
3,3-dimethyl-1-butanethiol
1°
2°
1°
SH
2,2-dimethyl-3-butanethiol
SH
4°
1°
1°
1°
1°
SH
2-ethyl-1-butanethiol
Derivatives of 2,3-dimethylbutane
1°
2°
3°
1°
1°
1°
3-methyl-1-pentanethiol
2°
2°
2°
2,2-dimethyl-1-butanethiol
Here follow the perspective views of the enantiomers of the indicated structures:
2-hexanethiol
H
C
H3C
(R)
H
nBu
SH
C
H 3C
(S)
2-methyl-1-pentanethiol
H
C
H3C
(R)
nPr
CH2SH
C
H 3C
(R)
sBu
SH
(S)
C
(R)
C
CH2SH
nPr
Et
(R)
nPr
SH
Et
(S)
SH
nPr
H
C
iPr
SH
SH
iPr
Et
(S)
3-methyl-1-pentanethiol
H
H
H
C
H3 C
C
Et
H
4-methyl-2-pentanethiol
H
H
2-methyl-3-pentanethiol
H
C
H 3C
SH
nBu
3-hexanethiol
H
(S)
C
SH
sBu
H3 C
(R)
Et
C2 H4SH
C
H3C
(S)
C2H4SH
Et
3-methyl-2-pentanethiol
H
CH3
SH
(S)
(S)
Et
Me
H
CH3
SH
H
(R)
(S)
Me
Et
H 3C
(R)
2.
iPr
CH2SH
C
H3 C
(S)
(R)
(R)
Me
Et
H
H
C
CH2SH
iPr
H3 C
(R)
H
tBu
SH
Write condensed structural formulas for the following molecules:
N O2
H3 C
(a) (E)-2-bromo -1-nitropropene
Br
H
H
H3C
Br
(b) (2Z,4E)-5-bromo -2,4-nonadiene
F3 C
(c) (E)-3-methyl-2-trifluoromethyl-2-pentene
H3 C
CH3
C
H3C
SH
CH3
H
2,2-dimethyl-3-butanethiol
2,3-dimethyl-1-butanethiol
H
H
C
(S)
Et
Me
H
SH
CH3
H
(S)
SH
tBu
(S)
H
3.
How many stereoisomers exist for each of the following compounds? Draw Fischer diagrams, followed by perspective
diagrams (in a stable conformation) of each stereoisomer, and assign the absolute configuration at each stereogenic centre
(chiral carbon atoms) using the (R,S) nomenclature.
a)
O
b)
OH
OH
OH
HO
OH
O
HO
O
H
OH
tartaric acid
OH
five-carbon acyclic sugar (e.g. ribose)
(a) There are three stereoisomers of tartaric acid, (R,R); (S,S) and meso.
CO2H
OH
R
HO
H
R
H
H
HO
CO2H
CO2H
HO
H
S
H
OH
R
OH
S
H
OH
S
H
HO
OH
R R
H
CO2H
CO 2H
HO2C
CO2H
S
S
HO2C
H
R,R
CO2H
H
CO2H
HO
H
OH
HO 2C
CO2H
S
S,S
OH
R
H
meso
3
(b) There are in all 8 (2 ) stereoisomers, because there are no meso forms.
O
H
O
C
H
OH
R
H
H
OH R
H
OH
R
HO
H
OH R
HO
H
S
H
R
R
H OH
O
R
HO H
H
H OH
HOCH2
S
HO H
H
O
C
H
H
S
H
HO
H
S
HO
CH2OH
HO H
S
R
H
H
H OH
H
HOCH 2
R
H OH
HOCH2
S
R
S
S
H
OH R
OH R
H
OH R
CH2 OH
OH O
HO
R S R
H
HOCH2
H
O
R R S
H OH
H OH
H OH
O
H
O
H
OH H
H
C
S
HO
H
S
HO
H
S
OH
R
HO
H
S
HO
H
S
H
S
H
OH R
HO
H
S
HO H
H
H
H
CH2 OH
OH O
HO
C
HO
HO
S
H
O
H
C
CH2 OH
C
OH R
H
R
O
OH R
CH2 OH
O
H
H
C
OH R
HO
H OCH 2
O
H
CH2OH
H OCH 2
H
C
O
S
HO H HO
H
H
HOCH 2
CH2 OH
CH2 OH
H
H
OH O
R S S
H OH HO
H
H
HOCH2
OH O
S S S
HO H
OH H
H
4.
Assign the absolute configuration of any chiral carbon atoms in the following molecule, using the (R,S) nomenclature. Is
the molecule itself chiral? Why or why not?
Br
Despite the two chiral carbon centers,
the molecule is achiral because of the
plane of symmetry.
(R)
Br
(S)
5.
Androsterone is a steroid (and functions as a male sex hormone). It is a trans fused ring compound with the following
structural features (hydrogen atoms shown are only those required to indicate the stereochemisty).
CH3 O
H3C H
HH
HO
H
H
Draw a perspective view of the most stable conformation of this compound (review Chapter 4 on fused rings). Then
identify all the stereogenic carbon atoms in the compound, and assign the absolute configuration of each one using the
(R,S) nomenclature.
Here is my answer:
H
H
H
(S) H
H
H
H
H
O
H
H
H
H
H
H
H
H
H
H
H
H
(S)
H
(S)
(R) H
H
O
H
(S)
H
H
(S)
H
H
(S)
H
H