Lab Report: Dehydration of an Alcohol (Exp. 4)
40 pts/max
Name: Shawn Vuong
The following alkenes are the major products of the dehydration of 4-methyl-2-pentanol. The order that they
appear in the gas chromatogram is in the order of their boiling points (highest bp – longest retention time).
CH3
CH3
CH
C
H2 C
CH2CH2CH3
H3 C
H
CH3
C
CH2
C
CH2
H3 C
C
CH2CH3
H
CH3
CH
H3 C
CH3
CH3
CH
C
C
H
H3 C
H
H
C
C
CH3
H
10 pts.
Alkene (IUPAC Name)
Retention Time
2-methyl-2-pentene
4 min 04 sec
10.9%
2-methyl-1-pentente
3min 48 sec
34%
Trans-4-methyl-2-pentene
3 min 33 sec
22.5%
Cis-4-methyl-2-pentene
3 min 25 sec
10.4%
4-methyl-1-pentene
2 min 54 sec
22.2%
Percentage in Product Mixture
1. Write a detailed mechanism for the acid-catalyzed dehydration of 4-methyl-2-pentanol that accounts for the
formation of all of the above alkenes. (Hint: More than one carbocation rearrangement may be necessary to account
for formation of all of the products.) (10 pts)
2. Why must the distillation temperature be kept below 90 oC during the dehydration of 4-methyl-2-pentanol?
(5 pts)
If the temperature would raise above 90 degrees Celsius the potential for water evaporation would increase.
Therefore, water could get into the product and defeat the purpose of the dehydration.
3. Which conclusions can be drawn from the IR-spectrum of the reaction mixture? (5 points)
According to the IR spectrum, there are molecules of molecular weight of 84 grams in the mixture. *All alkenes
products of 4-methyl-2-pentanol have a molecular weight of 84 grams.
4. Predict all of the alkene products that are expected (including stereoisomers and alkenes arising via carbocation
rearrangements) from dehydration of the following alcohols. Indicate which of these products should be the major
product of the reaction. (5 points)
a. 3-methyl-2-butanol
b. 2-methylcyclopentanol
c. 3-cyclohexen-1-ol
OH
HO
CH3
H3C
CH3
H3C
OH
__________________________________________________________________________
5. Open the UCAN program. Which process is depicted by the first curved arrow in the E1 animation? (3 pts).
Lewis Acid Base Dissociation *to produce a carbocation intermediate
Open the ORA program. How many reaction steps are shown on the animation “Carbocation
rearrangement:E1”? (2 pts).
There are four steps