- E1 stands for Elimination Unimolecular.
- This means that the rate of these reactions appears to depend only on the
- The rate of the disappearance of substrate = d[ substrate ]/dt = -k[ substrate
], negative slope asymptotic to both axis.
- The truth is that the rate of this reaction is really pseudo-first order
in substrate concentration because the concentration of solvent and acid
catalyst, which affect this reaction, don't change that much as the reaction
- These substitutions occur by a removal (ionization) of the leaving group
to make a carbocation intermediate.
- They share the same first step as an SN1 reaction.
- The carbocation intermediate loses a vicinal hydrogen to make an alkene.
- The electrophilic carbon must be sp3 hybridized.
- The hybridization of the carbocation intermediate of this process is sp2.
Factors:The rate of this reaction is affected by:
- The stability of the carbocation intermediate, rate greater for
tertiary > secondary >> primary, neopentyl
- Inductive effect
- Solvent, works best with polar protic solvents like water, alcohols, etc.
- A polar solvent is required for solubility.
- A protic solvent hydrogen bonds to the leaving group helping to
ionize it off.
- This means that E1 substitutions are really
pseudo-first order because the solvent has an effect on the rate but
its concentration does not change that much!
- Leaving group, works best with leaving groups that are weak bases
because they have a weaker bonds with carbon and can stabilize negative charge best.
- F > HO > H2N
- Sulfonate > I > Br > Cl > F
- right-down, more right than down
- cation > neutral
- Elimination over substitution is favored by heating and lack of a
- The alkene formed is the most stable, tetra > tri > 1,2-di > 1,1-di
> mono substituted alkene, following Saytzeff's rule, "the poor get
- This stability is explained by more electronegative sp2
carbons being more stabilized by alkyl groups than hydrogen.
- The stability is explained by more hyper-conjugation to groups
vicinal to the Pi bond.
- The stability is explained by placing a flat space between alkyl
- The diastereomer (E or Z) that is most stable is the one that has
less steric interactions.
SN1,SN2, and E1 Reactions of Alkyl
(the protic solvent)
Good Nucleophile that are not too basic
(cyanide, amines, alkanoates,
phosphines, sulfides, selenides,
||slowest SN2, no rxn
||slower SN2, no rxn
||slower SN2, no rxn
||slow SN1/E1 if heated, Saytzeff
||SN1/E1 if heated, Saytzeff
||slowest SN1/E1 if heated, Saytzeff