CH 237 Experiment 4?

docx

School

University of Alabama *

*We aren’t endorsed by this school

Course

237

Subject

Chemistry

Date

Jan 9, 2024

Type

docx

Pages

Uploaded by HighnessClover19320

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:

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

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.