Which elimination reactions, E1 or E2, depend on the concentration of the substrate? Is there a formation of carbocation in both elimination reactions, E1 and E2? Do E1 reactions require a strong base, like E2 reactions? Why does the rate of the E1 reaction depend only on the substrate? Is there a requirement for the stereochemistry of the starting material in E1 reactions? Other than this, the reactivity pattern is the same for both E1 and E2 — they go faster with more substituted alkyl halides:.
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Notify me of followup comments via e-mail. So, if we have a tertiary halide in presence of a strong base, the E2 will dominate over E1! Like every first one, this was a simpler example. Now we will see what happens to those more substituted compounds. They are a bit more complex. For example, if we have a more substituted alkyl halide, we have to pay attention to their stereochemistry. The first reaction is E1 elimination reaction. As a base, water is used, which is also a solvent.
Water is a weak base. Products are trisubstituted and disubstituted alkene. And the second reaction is E2 elimination reaction with a strong base sodium hydroxide and water as a solvent.
Products are trisubstituted and monosubstituted alkene. How do we determine which of these carbons will participate in the double bond? Using the Zaitsev rule! But when we draw all these products, we can see that disubstituted alkenes are the same when rotating the structure. These prefixes denote the number of carbon atoms attached to the double bond rounded red.
The rate of the E1 reaction depends only on the substrate , since the rate limiting step is the formation of a carbocation. Hence, the more stable that carbocation is, the faster the reaction will be. The rate of the E2 reaction depends on both substrate and base , since the rate-determining step is bimolecular concerted.
A strong base is generally required, one that will allow for displacement of a polar leaving group. The stereochemistry of the hydrogen to be removed must be anti to that of the leaving group; the pair of electrons from the breaking C-H bond donate into the antibonding orbital of the C- leaving group bond, leading to its loss as a leaving group. Can you see why now? As you can see, cyclohexane rings can cause some interesting complications with elimination reactions!
Reactions taking place in single step via a high energetic transition state are usually referred as concerted,,,,where as unimolecular refferes to molecularity of the reaction,i. Thank you for the helpful info. I had one question… do E1 reactions able to make cis and trans products like the ones that are common to E2 reactions? Hello James, I have been reading your articles for quite a while now. They are easy to comprehend and to-the-point. Is isotopic effect is observed in E-1 Reaction?
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