CH 6-7 Elimination Reactions – Part I
All SN1 reactions, and some SN2 reactions are accompanied
by Elimination Reactions to form alkene products:
-carbon
•The Nuc acts as a base,
grabbing an acidic -H.
•The stronger the base, the more
elimination product.
 carbon
C
+
C
+ Nuc-H + Lg
R
alkene
ELIMINATION PRODUCT
Keys to Interpreting Elimination Reactions
•In the substrate, where is the -carbon (contains Lg), and
the -C’s & -H’s? Double bond forms between -C & -C);
•Evaluate substrate structure: 1o, 2o, or 3o alkyl halide
•Is the nucleophile a weak or strong base; small or bulky?
•Mechanism(s)? (SN1&E1, SN2&E2, only SN2, only E2)
•Products? For Elimination Reactions: How many alkene
products are formed and what is the structure and
geometry of the alkene products (cis vs trans)?
The E2 Elimination Mechanism
•E2: “Elimination….Bimolecular”
•Rate = k [nucleophile] [substrate]
(2nd order reaction)
•Nucleophile is a strong base
•“Concerted” Mechanism:

•E2 may accompany an SN2 reaction (not always).
The E2 Elimination Mechanism – T.S.
