Organic Chemistry I Lab Report

Experiment 7: StereochemistryA. Build the chair confirmation of cyclohexane. Draw the Newman projection using the template
provided.
B. In the chair conformation of cyclohexane you built in problem A, remove an equatorial
hydrogen from one carbon and axial hydrogen from an adjacent carbon. Replace both
hydrogens with methyl groups. This new molecule is a stereoisomer of 1, 2 –
dimethylcyclohexane. Using the template provided draw the two conformations of 1, 2 –
dimethylcyclohexane.
Are the two conformers identical? ________ If no, circle one with the lower energy in the diagram
above.
Are the two methyl groups cis or trans each other?_________________
C. In the chair conformation of cyclohexane you built in problem A, remove an equatorial
hydrogen from one carbon and an equatorial hydrogen from the adjacent carbon. Replace both
hydrogens with methyl groups. This new molecule is a stereoisomer of 1,2 –
dimethylcyclohexane. Using the template provided, draw the conformers of this 1, 2 –
dimethylcyclohexane.
Are the two conformers identical? __________ If no, circle the one with the lower energy in the
diagram above.
Are the two methyl groups cis – or trans – to each other? ________________
D. In the chair conformation of cyclohexane you build in problem a, remove an equatorial
hydrogen from one carbon and an axial hydrogen from the third carbon away (there is one
carbon between the two with removed hydrogens). Replace one hydrogens with methyl group
and the other with an cyano group. This new molecule is a stereoisomer of 1-cyano-3methylcyclohexane. Using the templates provided, draw the two chair conformers of this 1cyano-3-methylcyclohexane.
Are the two conformers identical? ____________ If no, circle the one with the lower energy in the
diagram above.
Are the two methyl groups cis – or trans – to each other?________________
E. In the chair confirmation of cyclohexane you built in problem A, remove an equatorial hydrogen
from one carbon and equatorial hydrogen from the third carbon away (there is one carbon
between the two with removed hydrogens). Replace one hydrogens with methyl group and the
other with an cyano group. This new molecule is a stereoisomer of 1-cyano-3methylcyclohexane. Using the templates provided, draw the two chair conformers of this 1cyano-3-methylcyclohexane.
Are the two conformers identical? ______________ If no, circle one with the lower energy in the
diagram above.
Are the two methyl groups cis – or trans – to each other?
F. The (+) enantiomer of a compound displayed an observed rotation of -1.72° when
measured in a polarimeter with a 1 dm path length at a concentration of 0.02 g/ml.
Calculate the specific rotation for the (-)-enantiomer.
[α]D =
Observed rotation (degrees)
α
=
3
Pathlength, l (dm) × Concentration, c (g / cm ) l ×c
G. Build the following molecules and assign R/S-configuration to all chiral centers. Then determine
the absolute configurations of each without relying on the models and write R- or S- at the
arrows pointing to the chiral centers.
H. Build two 2-chlorobutane molecules shown below:
a. What is the stereochemical relationship of these two molecules?
i.
Enantiomers
ii.
Identical
iii.
Diastereomers
iv.
Other
b. Take the first model and switch any two substituents on the chiral center. What
is the stereochemical relationship now of these two molecules?
I.
i.
Enantiomers
ii.
Identical
iii.
Diastereomers
iv.
Other
Build two models of R-2-chlorobutane as shown in the Newman projections. Follow the
instructions and build models A and B.
Build two models of S-2-chlorobutane as shown in the Newman projections. Follow the instructions and
build models C and D.
Name all four models making sure to indicate R/S at the beginning of the name. Always start the
numbering of the parent chain from the end that gives the R-carbon a smaller number than the Scarbon.
1. Model A:
_____________________________________________________________________
2. Model B:
_____________________________________________________________________
3. Model C:
______________________________________________________________________
4. Model D:
______________________________________________________________________
5. Which two compounds represent meso compounds?__________________
6. Write yes where appropriate in the table below:
Models to Compare
Identical
Enantiomers
Diastereomers
A and B
A and C
A and D
B and C
B and D
C and D
J. Build two models of chlorocyclohexane as shown in the diagram below. Follow the instructions
and build model A and B. Ha and Hb are hydrogens. Place models A and B in the chair
conformation.
I.
Assign R- and S- configurations to all chiral centers in model A and B. Write R- or S- with
an arrow pointing to the corresponding chiral center in the structure.
II.
What is the stereochemical relationship between A and B? ______________ ( choose
from enantiomeric, diastereomeric, identical or other)
III.
Would a solution of A rotate polarized light? ________ What about B? _________ Why
or why not?_____________________________________________________________
IV.
How many constitutional isomers can be called cis-dichlorocyclohexane? ___________
Would any of these isomers rotate polarized light? ________________
K. Build the two models of chlorocyclohexane as shown in the diagram below. Follow the
instructions and build model A and B. Ha and Hb are hydrogens. Place models A and B in the
chair conformation.
I.
Assign R- and S- configurations to all chiral centers in model A and B. Write R- or S- with
an arrow pointing to the corresponding chiral center in the structure.
II.
What is the stereochemical relationship between A and B? ______________ ( choose
from enantiomeric, diastereomeric, identical or other)
III.
Would a solution of A rotate polarized light? ________ What about B? _________ If
both do, what is the relationship between the rotation of light?
IV.
How many constitutional isomers can be called trans-dichlorocyclohexane? ___________
Would any of these isomers rotate polarized light? ________________