Exercise 8: - Conformational analysis and nomenclature
of cyclohexanes
- The axial conformation of
fluorocyclohexane is 1.05 kJ/mol less stable than the
equatorial conformation.
What is the energetic cost of a 1,3-diaxial
hydrogen-fluorine interaction?
- trans-1,3-Di-tert-butylcyclohexane is one of the
few molecules that exists largely in a skew-boat conformation. Why?
- The
following table lists the steric strain due to one hydrogen - substituent
1,3-diaxial interaction in some monosubstituted cyclohexanes:
|
Substituent |
Strain
(kJ/mol) |
Substituent |
Strain
(kJ/mol) |
|
Cl |
1.09 |
CH3 |
3.56 |
|
Br |
1.15 |
CH3CH2 |
3.66 |
|
OH |
1.96 |
(CH3)2CH |
4,61 |
|
CH3O |
1.57 |
(CH3)3C |
~10 |
a.
Draw the most stable conformation of trans-1-chloro-3-methylcyclohexane:
b.
Justify
your decision using the principles of conformational analysis.
c.
One
of the two chair structures of cis-1-chloro-3-methylcyclohexane
is more stable than the other by 15.5 kJ/mol.
Draw the structure
of the more stable structure.
d.
Calculate
the energy cost of a 1,3-diaxial interaction between a
chlorine and a methyl group.
e. Draw the most stable conformation of cis-1-tert-butyl-4-isopropylcyclohexane.
f. Calculate the strain in this molecule.
- Name the following compounds :
a.
b.
c.
d.
