E1 Mechanism
Overview:
The general form of the E1 mechanism is as follows: 
B: = base
X = leaving group (usually halide or tosylate) In the E1 mechanism, the the first step is the loss of the leaving group, which leaves in a very slow step, resulting in the formation of a carbocation. The base then attacks a neighboring hydrogen, forcing the electrons from the hydrogen-carbon bond to make the double bond. Since this mechanism involves the formation of a carbocation, rearangements can occur.
An example of the E1 reaction:
Base Strength: A strong base not required, since it is not involved in the rate-determining step
Leaving groups: A good leaving group is required, such as a halide or a tosylate, since it is involved in the rate-determining step.
Rearangements: Since the mechanism goes through a carbocation intermediate, rearangements can occur.
E2 Mechanism
Overview:
The general form of the E2 mechanism is as follows: 
B: = base
X = leaving group (usually halide or tosylate) In the E2 mechanism, a base abstracts a proton neighboring the leaving group, forcing the electrons down to make a double bond, and, in so doing, forcing off the leaving group. When numerous things happen simultaneously in a mechanism, such as the E2 reaction, it is called a concerted step.
An example of the E2 reaction:
Base Strength: A strong base is required since the base is involved in the rate-determining step.
Leaving groups: A good leaving group is required, such as a halide or a tosylate, since it is involved in the rate-determining step.
Stereochemistry requirements: Must occur with antiperiplanar stereochemistry.
Electrophilic Addition to Alkenes Mechanism
| Overview: Electrophilic addition to alkenes takes the following general form:  nuc: = nucleophile
E+ = electrophile Electrophilic addition to alkenes starts with the pi electrons attacking an electrophile, forming a carbocation on the most stable carbon. A nucleophile then attacks the carbocation to form the product. There are many different kinds of such addition, including: - Hydroxylation
- Hydrogenation
- Halogenation
- Oxidative Cleavage
- Hydration
- Epoxidation
- Cyclopropanation
- Halohydrin Formation
Clearly, there are numerous kinds of products that can be formed as a result of this mechanism. Orientation of Addition: Electrophilic Addition adds to give the Markovnikov Product, with the nucleophile added to the more highly substituted carbon. This is because the carbocation intermediate is significantly stabilized by alkyl substituents. Example of electophilic addition to alkenes: First, formation of the carbocation on the most highly substituted carbon Followed by attack of chloride on the carbocation to give the addition product |
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