Reaction mechanism, E1 elimination reaction, one of the important reaction in organic chemistry.

1. School of Pharmacy,DAVV, Indore
Submitted by-
Lalit Dhakar
Roll. No. 2105
M.Pharm,1st Sem
Guided by-
Dr. Tamanna Narsinghani Mam
Professor, DAVV
Subject-Advance organic chemistry
Code-MPC-102T
Seminar presentation
Topic- E1 Elimination reaction

2. Index
 Introduction
 E1 elimination reaction
 Mechanism
 Orientation of E1 reaction
 Stereochemistry
 Energy level curve
 Factor affecting E1 reaction

3.  Introduction :-
• An elimination reaction is a type of chemical reaction where several
atoms either in pairs or groups are removed from a molecule.
The removal usually takes place due to the action of acids and bases or
action of metals. It can also happen through the process of heating at
high temperatures.

4.  There are two mechanisms of elimination (E2 and E1).
• E2 mechanism — bimolecular elimination
• E1 mechanism — unimolecular elimination

5.  E1 ELIMINATION REACTION :-
• E1 mechanism which is also known as unimolecular elimination,
• There is a formation of carbocation as an intermediate.
• This happens in the presence of a base which further leads to the formation of a pi-bond in the
molecule.
• In E1, the reaction rate is also proportional to the concentration of the substance to be transformed.
• It exhibits first-order kinetics

6. Mechanism:-
Step 1-
Step 2-
• Step 2- A proton is abstracted by the base from
the adjacent ß- carbon atom to give the alkene
• Reaction mechanism of E1 reaction is two step
process
• Step 1-Alkyl halide ionized to give the
carbonium ion

7.  Orientation of elimination. :-
• Zaitsev's Rule:-
• When an elimination reaction gives predominantly the most stable alkene, we say that the reaction follows
Zaitsev's rule.
• This rule, named after the Russian chemist A. N. Zaitsev (1841-1910),
• States that the most highly substituted alkene is the major product in an elimination reaction where more than
one alkene can form.
• Zaitsev also spelled Saytzeff, Saytsef, or Saytzev

8. • Hofmann rule:-
• According to this rule major product is always least substituted alkene.
• Major product is obtained from formed from ß-carbon which has maximum number of hydrogens.
• Product is known as Hofmann product.

9.  Stereochemistry :-
• With C+ both syn and anti elimination can occur,
• So E1 reaction forms both E and Z products
• ß-carbon is bonded to one or two H’s
• Product stability leads to stereoselectivity but not stereospecificity

10.  Energy level curve :-
• Transition state(T.S)- an imaginary molecule
and can not be isolated
• Intermediate-stable entity an d can be isolated
• A reaction is through an intermediate has to
surmount two energy barrier
• One for the conversion of the reactant to
intermediate(Eact1)
• Other for the conversion of intermediate into
product(Eact2).

11.  Factor affecting E1 reaction:-
A).Effect of alkyl group-
Reactivity order: (CH3)3C- >
(CH3)2CH- > CH3CH2- > CH3
Increasing rate of E1 reaction
Increasing stability of carbocations

12. • B).Leaving group:-
• The rate determining step of the E1 is breaking the C-LG bond.
• Therefore, there is a very strong dependence on the nature of the leaving group,
• The better the leaving group, the faster the E1 reaction will be.
• Weak base= good leaving group
• .Order of leaving group
• Fˉ<Clˉ<Brˉ<Iˉ
• C).base:-
• The base is not involved in the rate determining step,
• The nature of the base is unimportant in an E1 reaction.

13. • D).Type of solvent:-
• Have dipoles due to polar bonds o can H atoms that can be donated into a H-bond.
• Anions will be solvated due to H-bonding,
• Polar protic solvents will stabilize a carbocation better, therefore promote an E1 reaction.
• Water, methanol,
• Ethanol,
• Isopropyl alcohol,
• Acetic acid.

14.  Application :-
• Conversion of mono enes into dienes and trienes.
• Conversion of vitamin A1 to vitamin A2

15.  Reference :-
• Morrison and Boyd's advance organic chemistry sixth edition
• March’s advance organic chemistry, sixth edition.