Monday, April 13, 2020

Time As A Determinate Of Final Product In A Dehydration Reaction Essay

Time As A Determinate Of Final Product In A Dehydration Reaction Time as a Determinate of Final Product in a Dehydration Reaction Robert Simack, Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, Alaska. Abstract: This study involved acid dehydration of 2-methylcyclohexanol. The results varied depending on the time elapsed after initial reaction. I attempted to prove the Evelyn Effect, which stated that over a period of time the products of the aforementioned reaction will beobserved to change volume so that those products formed by a cis isomer of 2-methylcyclohexanol will form first. However, once all molecules in the cis isomer undergo reaction the remaining trans configured 2-methylcyclohexanols will proliferate during the latter period of the reaction. I also postulated as to the possible formulation of 1-ethylcyclopentene, and to the cause of such an event. Introduction: After researching acid-catalyzed dehydration reactions (McMurray) and background on the Evelyn Effect (Clausen) I hypothesize that the cis isomer of 2-methylcyclohexanol will react via an E1 type process forming 1-methylcyclohexene according to predictions from Zaitzev's rule (Lehman). This should be due to the fact that the cis isomer has 2 anti-coplanar hydrogens. These two hydrogens should make the molecule more reactive. The trans isomer, with only one anti-coplanar hydrogen, should be slower to react and will form a 3-methylcyclohexene. In addition the 1-ethylcyclopentene will be formed from both the cis and trans isomers but only if the hydroxyl group is in an equatorial position. In that position electrons from the ring may attack the alcohol directly from behind pushing it off the ring and forming a five-membered ring instead. Results the ratio was roughly 6:1 trans/cis. Finally, in the spectra of the third fraction the cis isomer was absolutely imperceptible while the integration of trans was nearly twice that of the integration from fraction one. These spectra show that cis reacted first and was quickly consumed by the reaction leaving trans isomers to finish the reaction. Because it is known that the reaction with cis starting material caused both 3-methylcyclohexene and 1-methylcyclohexene I postulated that the foremost product of the latter stages of the reaction must be 3-methylcyclohexene, which is the sole product of the trans reaction (McMurray, chap. 11.12). In addition to the cis and trans peaks the peaks for both 3-methylcyclohexene and 1-methylcyclohexene could be found on the spectra at 5.7 and 5.4 respectively. The NMR showed that the integration of 1-methylcyclohexene dropped only slightly throughout the reaction while the integration of 3-methylcyclohexene increased nearly tenfold. The fi ndings from the spectra prove the hypothesis that the cis reaction will go the fastest followed by the trans because as the cis is consumed it's peak at 3.79 will decrease as well as the peak for 1-methylcyclohexene due to termination of that products formation. Also, peaks for 1-ethylcyclopentene begin to show in the spectra for the second fraction and increase in size (area beneath the peak) by the spectra of the third fraction. At the root of this phenomena is steric hinderance. Both the cis and trans isomers will form 1-ethylcyclopentene (fig. 1). However, because of steric hinderance the trans isomer is favored to form the 1-ethylcyclopentene. This fact will explain why more of the pentene shows up in the third fraction. Finally, a tiny peak showed at 4.6 in every fraction's spectra indicating the presence of methylenecyclohexane. This product formed from the original product by acid catalyst. Experimental: An apparatus was constructed with a round bottom flask topped by a claisen adaptor in which