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Final Lab Report
Name_________________________________
Exp. 3: Stereochemistry and Molecular Modeling of Cyclohexanes
EXPERIMENTAL RESULTS
(Complete in pencil or pen!)
Part 1: Review of Concepts
For the following statements, FILL IN THE BLANKS using a term from the list below.
chair conformation
equatorial
axial
torsional
angle
1,3-diaxial interactions
tetrahedral
ring flip
steric
equilibrium
1. _______________________ strain is due to expansion or compression of bond angles, resulting in a
deviation of the preferred 109.5o angle preferred in a ________________________ carbon.
2. ________________________ strain is due to eclipsing of bonds on neighboring atoms.
3. ________________________ strain is due to the repulsive interactions which occur when atoms
approach each other too closely.
4. Cyclohexane is found in the ________________________________ most of the time, as this form has
no torsional strain and very little angle strain.
5. Each carbon atom in a cyclohexane ring can bear two substituents. One substituent is said to occupy an
________________________ position, and the other substituent is said to occupy an
________________________position.
6. When a ring bears one or more substituents, the substituents can occupy either axial or equatorial
positions, and these two conformations are at ________________________ with each other.
7. The term _________________________is used to describe the conversion of one chair conformation
into the other.
8. Axial substituents generate ________________________________, a form of steric hindrance;
therefore bulkier substituents generally prefer the equatorial position.
Part 2: Drawing a Chair Conformation
1. Draw a wide V.
2. Draw a line going
down at a 60o angle,
ending just before the
center of the V.
3. Draw a line parallel to
the left side of the V
ending just before the
left side of the V.
9. In the provided space, draw a chair conformation.
4. Draw a line parallel
to the line from step 2,
going down exactly as
low as that line.
5. Connect the dots.
Chair conformation
Part 3: Drawing Axial and Equatorial Positions
1. Draw all axial
positions as parallel
lines, alternating in
directions.
2. Draw all equatorial positions as pairs of parallel lines.
SUMMARY: All
substituents are drawn
like this:
parallel with
this side!
a
a
e
a
e
e e
e
a
e
a
a
10. In the provided space, draw a chair conformation showing all six axial positions and all six equatorial
positions LABELED.
Chair conformation w/substituents
Part 4: Drawing Both Chair Conformations of a Monosubstituted Cyclohexane
1. Draw a chair
conformation.
2. Place the substituent in
an axial position.
3. Draw the ring flip and the axial group becomes equatorial.
Br
Br
1
2
1
axial
axial
2
equatorial
2
11. In the provided space, draw both chair conformations of methylcyclohexane.
methylcyclohexane—before and after ring flip
12. In the provided space, draw both chair conformations of tert-butylcyclohexane.
tert-butylcyclohexane—before and after ring flip
1
Br
Part 5: Drawing Both Chair Conformations of a Disubstituted Cyclohexane
1. Using a numbering system, determine the location
and configuration of each substituent. Draw the
structure using solid and dashed lines to indicate
relative (cis vs. trans) stereochemistry.
Br
2. Place the substituents on the first
chair using the info from step 1.
3. Draw the second chair skeleton, and
place the substituents using the info
from step 1.
Br
H
Bromine is at C-1
and is UP
1
3
1
2
2
H
H
1
Br
3
2
CH2CH3 H
CH2CH3
3
CH2CH3
Ethyl is at C-3
and is DOWN
13. In the provided space, draw both chair conformations of trans-1-chloro-4-methylcyclohexane.
Relative stereochemistry
1-chloro-4-methylcyclohexane—before and after ring flip
Part 6: Comparing Stability of Chair Conformations
1. Using a numbering system,
determine the location and
configuration of each substituent.
2. Using the information from step
1, draw both chair conformations.
Ethyl is at C-1
and is UP
CH2CH3
2
5
Cl
8.0 kJ/mol
CH2CH3
CH2CH3
5
Cl
CH3
1
3. Assess the energy cost of each axial group.
Methyl is at C-2
and is UP
3
3
4
CH3
2
4
5
Cl
3
CH3
2
Cl
3
2
CH3
Total energy cost =
8.0 kJ/mol
1
CH2CH3
7.6 kJ/mol
4
5
CH3
1
4
4
Chlorine is at C-5
and is DOWN
5
1
3
2
Cl
CH2CH3
1
2.0 kJ/mol
Total energy cost =
9.6 kJ/mol
14. In the provided space, draw both chair conformations of cis-1-chloro-2-methylcyclohexane, calculate
the total energy strain of each, and circle the most stable conformer.
Relative stereochemistry
cis-1-chloro-2-methylcyclohexane—before and after ring flip
15. In the provided space, draw both chair conformations of trans-1-chloro-3-methylcyclohexane, show
the total energy strain of each in the provided box, and then circle the most stable conformer.
Relative stereochemistry
trans-1-chloro-3-methylcyclohexane—before and after ring flip
Chair 1:
Total Strain Energy (kJ/mol)
Chair 2:
Total Strain Energy (kJ/mol)
16. In the provided space, draw both chair conformations of cis-1-tert-butyl-4-ethylcyclohexane, show the
total energy strain of each in the provided box, and then circle the most stable conformer.
cis-1-tert-butyl-4-ethylcyclohexane —before and after ring flip
Relative stereochemistry
Chair 1:
Total Strain Energy (kJ/mol)
Chair 2:
Total Strain Energy (kJ/mol)
1,3-DIAXIAL INTERACTIONS FOR SEVERAL COMMON SUBSTITUENTS
SUBSTITUENT
-Cl
-OH
-CH3
-CH2CH3
-CH(CH3)2
-C(CH3)3
STERIC HINDRANCE FROM
1,3-DIAXIAL INTERACTIONS
(kJ/mol)
2.0
4.2
7.6
8.0
9.2
22.8