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10.4 The E1 Mechanism
Concentration of the base doesn't affect the rate because the base doesn't participate in this step.
The step is said to be unimolecular because it involves only one chemical entity.
The first step of an E1 process is the same as the first step of an S 1 process.
The main factors that affect the competition between substitution and elimination reactions will be explored at the end of this chapter.
The rate of an E1 process is affected by the effect of the substrate.
The rate is very sensitive to the nature of the starting alkyl halide, with tertiary halides reacting more readily than secondary halides, and primary halides do not undergo E1 reactions.
The reason for the trend is the same as the one we saw for S 1 reactions.
The same thing happens with an E1 process.
The regiochemical preference for the Zaitsev product is the same as it was for the E2 reactions.
The major product is the more-substituted alkene.
The regiochemical outcomes of E1 and E2 reactions are different.
The regiochemical outcome of an E2 reaction can be controlled by carefully choosing the base.
The Zaitsev product is usually obtained.
Stereospecific E1 reactions are not the case.
They don't need antiperiplanarity in order for the reaction to occur.
Stereoselective E1 reactions are possible.
In competition are substitution and elimination reactions.
Predicting the products of a reaction requires you to determine which mechanism won the competition.
There is a clear winner in some cases.
E2 wins the competition and no other mechanisms can compete.
An S 2 process can't occur at a reasonable rate because the substrate is tertiary.
It is a slow step to form a carbocation.
If the competing E2 process is very slow, the competition is very strong.
When a strong base is used, E2 occurs quickly, so E1 and S 1 can't compete.
Don't fall into the trap of thinking that there is always a winner.
Sometimes there is, but sometimes there are more than one product.
Determine the function of the reagent.
Determine the expected mechanism by analyzing the substrate.
Regiochemical and stereochemical requirements should be considered.
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