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evelyn effect wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 background on discovery 2 dehydration of 2 methylcyclohexanol or 4 methylcyclohexanol 3 possible explanations of different ratio formations 4 additional study on the evelyn effect 5 references toggle the table of contents evelyn effect add languages add links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia chemical phenomenon the evelyn effect is defined as the phenomena in which the product ratios in a chemical reaction change as the reaction proceeds this phenomenon contradicts the fundamental principle in organic chemistry by reactions always go by the lowest energy pathway the favored product should remain so throughout a reaction run at constant conditions however the ratio of alkenes before the synthesis is complete shows that the favored product is not the favored product the basic idea here is that the proportions of the various alkene products changes as a function of time with a change in mechanism 1 background on discovery edit professor david todd at pomona college was testing the dehydration of 2 methylcyclohexanol or 4 methylcyclohexanol c 1994 and unexpectedly interrupted the alkene distillation midway to have lunch with his secretary evelyn jacoby after lunch he continued his distillation but kept the early products separate from the completed ones the analysis showed two different alkene ratios the reaction products and pathways to the products seem to have changed over time dr todd called this phenomenon the evelyn effect 2 3 dehydration of 2 methylcyclohexanol or 4 methylcyclohexanol edit a simple example of the evelyn effect is the sophomore level chemistry lab experiment involving two popular examples that are listed below a dehydration of 4 methylcyclohexanol 2 dehydration of 4 methylcyclohexanol jpeg b dehydration of 2 methylcyclohexanol 4 dehydration of 2 methylcyclohexanol jpeg c mechanism for the dehydration of 2 methylcyclohexanol 4 possible explanations of different ratio formations edit in general if more than one alkene can be formed during dehalogenation by an elimination reaction the more stable alkene is the major product there are two types of elimination reactions e1 and e2 an e2 reaction is a one step mechanism in which carbon hydrogen and carbon halogen bonds break to form a double bond c c pi bond an e1 reaction is the ionization of the carbon halogen bond breaking to give a carbocation intermediate then the deprotonation of the carbocation for these two reactions there are 3 possible products 3 methyl cyclohexene 1 methyl cyclohexene methylene cyclohexane the production of each of these occurs at different rates and the ratios of these also change over time it is well known that the dehydration of the cis isomer is 30 times faster than the trans isomer it then appears that the reaction proceeds mainly by a trans mechanism and following the zaitsev rule 1 methylcyclohexene is preferentially formed in the early stages of the reaction indeed if only about 10 of the total distillate is collected as the first fraction one finds that the alkene is about 93 l methylcyclohexene at the end of the distillation one finds a value as low as 55 of l methyl isomer from these results the phenomenon of the evelyn effect can be observed and a conclusion can be drawn that a change of mechanism occurs somewhere during the synthesis additional study on the evelyn effect edit a kinetic and regional chemical study of the evelyn effect has been described the results in the journal of chemical education made claims involving the mechanism by which the dehydrations occurred the article looks into the claim of having e1 and e2 mechanisms occur in the reaction the researchers measured the kinetics of the formation of a 3 degree carbocation s and compared them to theoretical calculations that would occur if the experiment ran as an e2 reaction instead the reaction showed a mechanism that initially formed a 2 degree carbocation utilizing an e1 pathway their conclusion was that the mechanism is neither e1 or e2 but rather e 2 like exhibiting first order kinetics 5 references edit the dehydration of 2 methylcyclohexanol revisited the evelyn effect david todd j chem educ 1994 71 5 p 440 doi 10 1021 ed071p440 publication date may 1994 1 2 wong crispin currie james 2001 chapter 5 the evelyn effect teaching with cache molecular modeling in chemistry pdf pacific university archived from the original pdf on 4 march 2016 todd david may 1994 the dehydration of 2 methylcyclohexanol revisited the evelyn effect journal of chemical education 71 5 440 bibcode 1994jched 71 440t doi 10 1021 ed071p440 1 2 dr kalju kahn department of chemistry and biochemistry uc santa barbara 2007 http www chem ucsb edu kalju chem226 public pcgamess_tutorial_a1 html the acid catalyzed dehydration of an isomeric 2 methylcyclohexanol mixture a kinetic and regiochemical study of the evelyn effect journal of chemical education january 1997 74 1 pg 102 retrieved from https en wikipedia org w index php title evelyn_effect oldid 1356108915 categories alkenes physical organic chemistry hidden categories articles with short description short description matches wikidata this page was last edited on 25 may 2026 at 20 18 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile view search search toggle the table of contents evelyn effect add languages add topic