Additional Problems for practice:
1. Draw the two chair conformations of cis and trans-1-chloro-2methylcyclohexane.
Cl
Me
Me
Cl
cis-1-chloro-2-methylcyclohexane
H
Me
Cl
Me
H
H
H
Cl
trans-1-chloro-2-methylcyclohexane
In each case, which is more stable? By how much (use table 3-6 in text)
ΔG = -RTlnKeq
1.7 kcal/mol
0.5 kcal/mol
Cl
Me
Keq=0.13
ΔG=1.2 kcal/mol
Me
Cl
88.5%
11.5%
more stable
1.7 kcal/mol +
0.5 kcal/mol
H
Keq=0.025
Me
Cl
Me
ΔG=2.2 kcal/mol
H
H
H
97.5%
more stable
diequatorial
0kcal/mol
Cl
2.5%
2.2 kcal/mol
2. Which isomer is more stable, cis or trans decalin? Explain your answer
in terms of the steric interactions of the two molecules.
H
No 1,3 diaxial interactions
H
trans-decalin (rigid)
H
H
H
H
H
H
H
H
cis-decalin
cis-decalin
extensive 1,3-diaxial interactions
Thus, trans-decalin is more stable than cis-decalin
3. Draw the following disubstituted cyclohexanes and label the
substituents as axial or equatorial. The substituents can be any alkyl
group of your choosing. Remember to include the ring-flip structure as
well.
(a) 1,3 trans disubstituted
(b)1,3-cis disubstituted
(c)1,5-cis disubstituted
(d) 1,4-cis disubstituted
(e) 1,5-trans disubstituted
(f) 1,6-trans disubstituted
ax
a
eq
ax
eq
ax
ax
b
eq
eq
ax
eq
ax
c
eq
ax
ax
d
eq
eq
ax
e
eq
eq
ax
ax
eq
f
eq
ax