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12/25/21
Virtual Experiment 7
Dehydrating Cyclohexanol
Pages 103-108 and 114-116 in the lab textbook
YouTube videos:
https://www.youtube.com/watch?v=09CDqovJgKA and
https://www.youtube.com/watch?v=vBMGNzRYngk.
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1
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Dehydration of Cyclohexanol
• In Exp. 7, cyclohexanol is dehydrated to form cyclohexene and water.
Two catalysts are used: H3PO4 (phosphoric acid) and H2SO4 (sulfuric
acid).
H
H
OH
H2SO4 (cat.), H3PO4 (cat.)
H
heat
cyclohexanol
H
+
H2O
H
cyclohexene
2
2
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12/25/21
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Mechanism of This Reaction
• The first step of the reaction is the protonation of the hydroxyl group. The
OH group is not a leaving group; it must be first converted to a relatively
good leaving group, H2O.
• The protonation of the hydroxyl group in the reaction is accomplished using
H3PO4 and H2SO4. These acids are catalysts of this transformation. H2SO4 and
H3PO4 react with H2O to form H3O+.
H
O
O
H
H
H
H2O
+
+ H O
H
base-2
acid-2
base-1
acid-1
• This step is an acid-base equilibrium.
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3
Mechanism of The Reaction, contd.
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• In the second step, the leaving group HOH takes off, and a relatively
stable secondary carbocation is formed. This is a rate-determining
(i.e., slowest and most difficult) step of the overall reaction. HOH is
a relatively good leaving group because it is a conjugate base of the
very strong acid H3O+ (pKa = -2).
H
H
O
H
H
HOH
+
4
4
2
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Mechanism of the Reaction, contd.
5
• The third step is the formation of cyclohexene, an alkene:
H
β
H
H
+
O
H
H
+
H
H3O
H
cyclohexene
base
• H2O acts as a (weak) base removing one of the four b-protons (only
two of them are shown in the scheme above). H3O+ is regenerated and
it can be used again in the reaction with the next molecule of
cyclohexanol.
• The described mechanism is called the Unimolecular Elimination, E1.
This mechanism is valid for dehydration of 2o and 3o alcohols.
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Reaction of Cyclohexene with Br2
• To prove that the compound obtained in the experiment is an
alkene, the product can be checked for the presence of a C=C bond
using bromine:
H
+ Br-Br
H
colorless
red
Br
H
Br
H
colorless
Br
H
H
Br
+
H
Br
H
Br
• If the product is an alkene, the red color of Br2 will disappear
(assuming that you do not use excess Br2). Note that alcohols do
not react with Br2.
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Dr. I. Smoliakova
Chem 340L, Survey of Organic Chemistry Lab
Experiment 7
Dehydrating Cyclohexanol
The following are the major steps of Experiment 7:
read and understand the experiment description on pages 103–108 (the experiment background and
the description of the semi-microscale dehydration) and 114–116 (the product characterization using
bromine) of the lab textbook,
(ii)
watch two YouTube videos by clicking on the following links:
https://www.youtube.com/watch?v=09CDqovJgKA and

(iii)
write Report 7 (see the guidelines below) and upload the scanned document as a pdf file into
Blackboard, and
(iv)
take Quiz 7 on Bb before the deadline.
If you have questions, contact Dr. Smoliakova or your TA.
(i)
Guidelines for Quiz 7 (a total of 10 pts)
1. Reaction equations for a) the dehydration of cyclohexanol using H2SO4/H3PO4 as catalysts and b) the
reaction of cyclohexene with bromine. Anti-addition of bromine to alkenes. Color change during alkene
bromination.
2. The mechanism of cyclohexanol dehydration.
3. Structures and names of the compounds, which can be used as catalysts in the dehydration reaction.
4. Names, structures, hazards, and roles (e.g., a reagent, solvent, product, catalyst, drying agent, etc.) of all
compounds used in the online experiment and recommended in the textbook.
5. The density of cyclohexanol and cyclohexene relative to the water density. Immiscibility of
cyclohexanol and cyclohexene in water.
6. IR spectra of alcohols and alkenes. Expected wavenumbers for stretching vibrations of (sp3)C-H, (sp2)CH, (sp3)C-(sp3)O, C=C, and (sp3)O-H bonds. (See Chapter 11 and Table 11.3 in the Chem 340 textbook for
help.)
7. Major steps of the procedure described in the lab textbook and used in the videos.
8. Equipment, apparatus, and glassware used in the experiments.
9. Safety issues during the experiment.
Guidelines for Report 7 (a total of 30 pts)
Your report will consist of three parts.
Part 1 of the report should consist of the following (a total of 10 pts):
a. (1 pt) Write your name, section/subsection number, date, and the number and name of the
experiment.
b. (1 pt) What is(are) the purpose of the experiment?
c. (8 pts) Draw and complete the Table of Properties. To calculate the theoretical and actual yield of
the product, use the amounts given in the Table below. (Do not use the amounts provided in the
video and the lab textbook.)
* This document was prepared by Dr. Smoliakova and used with her permission
1
Dr. I. Smoliakova
Chem 340L, Survey of Organic Chemistry Lab
Table of Properties
Name of the
Compound
Lewis
Physical Molec. Amount Used (or Density,
Structure State and Mass
to Be Prepared
g/mL
Assuming the 100%
of the
Appea(for
Yield) in g (for solids) liquids)
Compound
rance
Amount Used
in Moles
Hazards*
or mL (for liquids)
cyclohexanol
(reactant)
cyclohexene
(product)
Sulfuric
acid
(catalyst)
phosphoric
acid
(catalyst)
bromine
(reagent)
trans-1,2dibromocyclohexane
6.0 mL
Calculate and write
down the theoretical
yield of the product
in grams
Calculate and
write down the
theoretical yield
of the product in
moles
n/a
0.4 mL
n/a
n/a
n/a
0.8 mL
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
* Please note that the statements like “eye contact,” “skin contact,” etc., are not HAZARDS. You need to
be specific and correct. Also, students providing false data in the report, including false data about hazards,
will be graded according to the course syllabus’s rules.
Do not forget to show your calculations in the report below the Table!
Part 2. (a total of 10 pts)
Describe everything that the chemists did during the experiments shown in the two videos. You should
use the past tense. Write complete sentences in paragraph form. Be concise (limit your writing to 1
page). Be sure to use the correct names of all pieces of equipment and all steps of the procedures. (8 pts
for the dehydration experiment and 2 pts for the bromination)
Part 3. (a total of 10 pts)
a. (2 pts) Write the equations of two reactions: 1) the dehydration of cyclohexanol in the presence of
phosphoric and sulfuric acids and 2) cyclohexene reaction with bromine. Indicate the role of each
compound in the reaction (e.g., a reagent, product, catalyst, or solvent).
b. (2 pts) Calculate the percent yield of cyclohexene, assuming that someone did the dehydration
experiment using the amounts shown in the Table of Properties on page 2 of this document and
obtained 4.00 mL of cyclohexene. All calculations must be shown.
c. (2 pts) Your instructor believes that the chemist who did the dehydration experiment in the video
violated safety rules. Can you mention a couple of the safety rule violations?
d. (a total of 4 pts) Consider two IR spectra shown on the next page and marked as A and B. One of
them belongs to cyclohexanol, and the other belongs to cyclohexene.
(i)
(1 pt) Which spectrum belongs to cyclohexanol, and which to cyclohexene?
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Dr. I. Smoliakova
(ii)
Chem 340L, Survey of Organic Chemistry Lab
(3 pts; 6 ´ 0.5 pt for each correct signal assignment) Assign each signal marked with a
number to a specific bond and vibration type. The carbon hybridization must be indicated in
your answers, for example: (sp)C-H bond bending vibrations, (sp2)C-H bond stretching
vibrations, etc.
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