Organic Chemistry: Sn2E2 Reactions

Study Guide

Terms

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Terms

β-elimination

A mechanism that involves the removal of a beta-hydrogen. All E2 reactions are β-eliminations.
Antiperiplanar

If two bonds define two line segments, then they are antiperiplanar if they are antiparallel in the plane they define. It's much easier to see antiperiplanar bonds than it is to explain them. In the following diagram, the C-H and C-LG bonds are antiperiplanar:

E2 reactions require an antiperiplanar β-hydrogen.
Backside Attack

The S_N2 mechanism in which the nucleophile attacks the α-carbon from a direction directly opposite to the C-LG bond. Results in inversion of stereochemical configuration.
Concerted

A single step mechanism. The S_N2 and E2 mechanisms are concerted.
E2

An E2 reaction in which a β-hydrogen and a leaving group are removed to form a double bond. The reaction is so named because it is bimolecular (2 molecules) and because it involves the Elimination of a β-hydrogen. See the $\mbox{E2}$ section.
Frontside attack

A disproved S_N2 mechanism in which the nucleophile attacks the α-carbon from the same side as the C-LG bond. If this mechanism was valid, it would result in retention of stereochemical configuration. See backside attack.
Intramolecular

A reaction that involves groups attached to the same molecule. Contrast with the intermolecular reaction, which takes place between groups on two different molecules.
S_N2

A S_N2 reaction is a bimolecular (2 molecules) reaction involving the Substitution of a Nucleophile for a leaving group. See the $\mbox{S}_{\mbox{N}}2$ section.
Saytzeff's rule

Saytzeff's rule states that an E2 reaction will preferentially form the most stable alkene isomer. Alkene stability generally increases with branching at the alkene carbons.

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