CH 237 Experiment 4?
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Experiment 4
CH 237-012
Experiment 4: Dehydration of Methylcyclohexanols
Introduction:
The dehydration of 2-methylcyclohexanol to yield a mixture of alkenes is a classic experiment
frequently conducted in college organic chemistry laboratories. This reaction serves as a practical
demonstration of Zaitsev's rule and the E1 mechanism in alcohol dehydration. However, this
seemingly straightforward reaction gained notoriety when an unexpected phenomenon was
observed in 1994, leading to the coining of the term "The Evelyn Effect." Numerous mechanistic
hypotheses have been proposed to elucidate the causes of the Evelyn Effect. Yet, a definitive
explanation has remained elusive. This experiment seeks to investigate the existence of the
Evelyn Effect in the dehydration of 2-methylcyclohexanol and extends the inquiry to the
analogous compound, 4-methylcyclohexanol. By performing these dehydration reactions in the
presence of phosphoric acid and utilizing a simple distillation setup, we aim to collect two
fractions of the reaction products. Subsequent analysis via gas chromatography will allow us to
discern any variations in product composition and potentially shed light on the underlying
mechanisms responsible for the Evelyn Effect.
Results:
The final yield mass of the product (actual yield) of flask 1 and 2 were obtained for both 2- and
4-methylcyclohexanol and measured as:
2-methylcyclohexanol
o
Flask 1 (alkene volume 8 ml): 4.37 g
o
Flask 2 (alkene volume 6 ml): 3.69 g
4-methylcyclohexanol
o
Flask 1 (alkene volume 8ml): 4.76 g
o
Flask 2 (alkene volume 6 ml): 3.30 g
The values were used to calculate the following:
Theoretical Yield:
2-methylcyclohexanol:
(
150
mmol cyclohexanol
)
(
1
mol
1000
mmol
)(
1
molcyclohexene
1
molcyclohexanol
)(
96.2
methylcyclohexene
1
mol
)
=
14.43
gmethylcyclohexe
4-methylcyclohexanol:
(
150
mmol cyclohexanol
)
(
1
mol
1000
mmol
)(
1
molcyclohexene
1
molcyclohexanol
)(
96.2
methylcyclohexene
1
mol
)
=
14.43
gmethylcyclohexe
Percent Yield:
2-methylcyclohexanol:
4.37
g
+
3.69
g
14.43
g
×
100%
=
55.85%
4-methylcyclohexanol:
4.76
g
+
3.30
g
14.43
g
×
100%
=
55.85%
Boiling Range for 2-methylcyclohexanol: 82°C-97°C
Product Composition:
Fraction 1 for 2-methylcyclohexanol:
Total Area: 2076623+68716830+15559152+267544 = 89020149
Percent of 3-methylcyclohexene= (2076623/89020149) x 100% = 2.33%
Percent of 1-methylcyclohexene= (68716830/89020149) x 100% = 77.19%
Percent of 2-methylcyclohexanol= ((15559152+267544)/89020149) x 100% = 20.47%
Fraction 2 for 2-methylcyclohexanol:
Total Area: 44829660 + 8199848 + 79785326 + 12818738 = 145633572
Percent of 3-methylcyclohexene= (44829660/145633572) x 100% = 30.78%
Percent of methylenecyclohexane= (8199848/145633572) x 100% = 5.63%
Percent of 1-methylcyclohexene= (79785326/145633572) x 100% = 54.78%
Percent of 2-methylcyclohexanol= (12818738/145633572) x 100% = 8.8%
Fraction 1 for 4-methylcyclohexanol:
Total Area: 62084266+8861396+2967949+9594243=83507854
Percent of 4-methylcyclohexene= (62084266/83507854) x 100% = 74.35%
Percent of 1-methylcyclohexene= (8861396/83507854) x 100% = 10.61%
Percent of 4-methylcyclohexanol= ((2967949+9594243)/83507854) x 100% = 15.04%
Fraction 2 for 4-methylcyclohexanol:
Total Area: 65277852 + 28379838 + 2508303 = 96165993
Percent of 4-methylcyclohexene= (65277852/96165993) x 100% = 67.88%
Percent of 1-methylcyclohexene= (28379838/96165993) x 100% = 29.52%
Percent of 4-methylcyclohexanol= (2508303/ 96165993) x 100% = 2.61%
In this experiment, all the methycyclohexene fractions were contaminated with the starting
alcohol. For fraction 1 of 2-methylcyclohexanol, alcohol contaminated 20.47%, and for fraction
2 of 2-methylcyclohexanol, alcohol contaminated 8.8%. In fraction 1 of 4-methylcyclohexanol,
alcohol contaminated 15.04% and for fraction 2, alcohol contaminated 2.61%.
Discussion:
This experiment was aimed to investigate the intriguing phenomenon known as the "Evelyn
Effect" in the context of the dehydration of 2-methylcyclohexanol and to ascertain whether a
similar time-dependent product ratio exists for 4-methylcyclohexanol. The analysis of gas
chromatography results provided compelling evidence that product distribution undergoes
substantial alterations over time, a hallmark of the Evelyn Effect. For 2-methylcyclohexanol, the
initial fraction (Fraction 1) exhibited a product composition of approximately 77.19% 1-
methylcyclohexene, with only 2.33% of 3-methylcyclohexene and 20.47% of 2-
methylcyclohexanol. In contrast, Fraction 2 displayed a significant shift in product distribution,
with approximately 54.78% 1-methylcyclohexene, 30.78% 3-methylcyclohexene, and 8.8% 2-
methylcyclohexanol. For 4-methylcyclohexanol, Fraction 1 primarily consisted of 74.35% 4-
methylcyclohexene, 10.61% 1-methylcyclohexene, and 15.04% 4-methylcyclohexanol. Fraction
2 displayed a different product distribution, with approximately 67.88% 4-methylcyclohexene,
29.52% 1-methylcyclohexene, and 2.61% 4-methylcyclohexanol. These findings clearly indicate
that the product distribution in the dehydration of both 2-methylcyclohexanol and 4-
methylcyclohexanol changes significantly over time. This observation is consistent with the
concept of the Evelyn Effect, where the reaction outcome varies as a result of temporal factors
such as equipment changes or other external influences. Mechanistically, the formation of 1-
methylcyclohexene from 2-methylcyclohexanol aligns with an E1 (elimination unimolecular)
pathway, involving the generation of a carbocation intermediate. Furthermore, the potential for
E2 (elimination bimolecular) mechanisms depends on the specific chair conformations of the
starting materials, with the trans isomers favored due to anti-coplanar arrangements. Remarkably,
the Evelyn Effect was pronounced in 2-methylcyclohexanol, with a distinct shift in product
distribution, while a more subtle time-dependent effect was observed in 4-methylcyclohexanol.
For 2-methylcyclohexanol, the E2 elimination would favor the trans isomer due to the anti-
coplanar arrangement of the hydrogen and the leaving group. For 4-methylcyclohexanol, the E2
elimination would also favor the trans isomer for similar reasons. This suggests that the Evelyn
Effect is more prominent in the former, possibly due to differing molecular structures and
reactivity. Ultimately, the interplay of E1 and E2 mechanisms, coupled with the influence of cis-
and trans-isomers, underscores the complexity of these dehydration reactions and their sensitivity
to external variables. The findings offer valuable insights into the dynamic nature of organic
transformations and the role of external factors in shaping product outcomes.
A detailed electron pushing mechanism for the formation of 1-
methylcyclohexene, 3-methylcyclohexene, and methylenecyclohexane
starting from 2-methylcyclohexanol assuming an E1 mechanism, would
appears as follows:
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A drawing of the most stable chair conformations of each of the four possible starting materials
would appears as follows:
The elimination products from each of these chair structures would appear as
follows:
Conclusion:
This experiment explored the phenomenon known as the "Evelyn Effect" during the dehydration
of 2-methylcyclohexanol and investigated whether a time-dependent product ratio exists for 4-
methylcyclohexanol. The results revealed clear evidence of the Evelyn Effect, with product
distribution changing significantly over time due to external factors or equipment changes.
Mechanistically, the formation of 1-methylcyclohexene from 2-methylcyclohexanol is consistent
with an E1 mechanism, while E2 pathways may also play a role. Notably, the Evelyn Effect is
more pronounced in 2-methylcyclohexanol, possibly due to differing molecular structures. This
experiment highlights the dynamic nature of organic transformations, emphasizing the impact of
external variables and providing insights into the complexity of these reactions.
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CH₁
2.
OH
a
Proton transfer
d
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b Lewis acid/base.
e E2 Elimination
g= SN2 Nucleophilic substitution
c = Electrophilic addition
The rections above involve synthesis or reactions of alcohols and ethers.
Identify the mechanism by which they proceed from among the mechanisms listed. Use the letters a- g for
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1.
2.
Submit Answer
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Click and drag to start
drawing a structure.
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☐
: ☐
+
х
G
0
H2SO4, H₂O
HgSO 4
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an enol
carbonyl compound
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●
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●
●
✓
?
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n [ ]#
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opy
aste
[*
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CH₂
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d E1 Elimination
-
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=
b = Lewis acid/base
e E2 Elimination
g = SN2 Nucleophilic substitution
c = Electrophilic addition
The rections above involve synthesis or reactions of alcohols and ethers.
Identify the mechanism by which they proceed from among the mechanisms listed. Use the letters a - g for
your answers.
1.
2.
Submit Answer
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H₂O
NaHCO3
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CH₂
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OH
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Br
+
retrosynthesis
NEC Na -NaBr
Synthons
C-C bond formation
synthetic equivalents
Br
D=00
CN
OH
||
ⒸC=N
H₂O, H+
hydrolysis
do not exist
exist
functional group transformation
Common synthons:
C1 synthons: carbon dioxide, carbon monoxide, cyanide, formaldehyde C2
synthons: acetylene, acetaldehyde
C₂H4OH synthon: ethylene oxide
OH
Carbocation synthons: alkyl halides, carbonyl C
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