Organic Chemistry: Sn2E2 Reactions
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
SN2
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
SN2
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
SN2
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.
SN2
-
A
SN2
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.





