Elimination reactions , Hoffman rule , Savtseff rule

1. ELIMINATION REACTION [E1 & E2 ; HOFFMAN
& SAYTZEFF’S RULE]
DEPARTMENT OF PHARMACEUTICAL SCIENCES, RTM
NAGPUR UNIVERSITY, NAGPUR
Presented by
Tahmina khan

2. CONTENT
■ Introduction
■ Basic Requirements of Elimination Reactions
■ E2 reaction
■ E1 reaction
■ Zitsev rule
■ Hoffman rule
■ Referance

3. Elimination Reaction-
■ An elimination reaction is a type of reaction in wich
two substituents are removed from a molecule in
either one or two step mechanism.
■ The one-step mechanism is known as the E2 reaction,
and the two-step mechanism is known as the E1
reaction
■ The numbers refer not to the number of steps in the
mechanism, but rather to the kinetics of the reaction:
E2 is bimolecular (second-order) while E1 is
unimolecular (first-order).

4. Basic Requirements of Elimination
Reactions-
1) Substrate –
A. For 1,2 elimination reaction the constituents required
are substrate which undergo and contains a good
leaving group.
B.The best choice for leaving group containing
substrate is alkyl halide. C. In substrate there should be
necessary to present beta hydrogens more than 1.

5. 2) Nucleophile Or Base –
In the reaction, base is required to abstract proton.
3) Solvent –
Also at a time solvent like water or alcohol required as a
solvent.

6. E2 Reaction-
■ E2 is a single step elimination, with a single transition
state.
■ The product of an E2 elimination reaction has one
more degree of unsaturation than the starting material
■ For instance, the base induced elimination of “HX” of
an alkyl haLide rise to an alkene
■ Ex

7. Mechanism
■ The most common mechanism for dehydrohalogenation is the
E2 mechanism. It exhibits second-order kinetics, and both the
alkyl halide and the base appear in the rate equation
rate = k[(CH),CBr||HO||
The reaction is concerted all bonds are broken and formed in a
single step.
E2 reactions are regioselective and favor the formation of
Zaitsev products.

8. Energy profile For an E2 reaction-

9. Reactivity of E2 reaction
1. Reactivity of E2 reactions depends on alkyl halide.alkyl
halide containing beta hydrogen must be needed.
2. The order of reactivity in E2 reaction is –
Tertiary RX > Secondary RX > Primary RX 3.
3. Tertiary alkyl halide is more active because it contains
more no.of beta hydrogens i.e 9 beta hydrogens

10. 4.Secondary alkyl halide conatins 6 and primary ones
contains 3 beta hydrogens.
5. If we start reaction with tertiary alkyl halide then we
get more substituated product so more is substituated
product more is stability hence tertiary alkyl halide most
reactive.

11. Orientation of E2 Reaction
■ In orientation of E2 reaction saytzeff rule is used to
show it.
■ Saytzeff rule is says that hydrogen is lost from that
carbon which have lesser number of hydrogens.

12. E1 Reaction-
■ It is a two-step process of elimination:
■ the first step is the loss of the leaving group, which
leave in a very slow step resulting in a formation of
carbocation is called “Ionization”.
■ In the second step the base attack the neighbouring
hydrogen, forcing the electron form The hydrogen
carbon bond to make the double bond the process is
called “Deprotonation”
■ Ex

13. Mechanism-
■ The E1 reaction proceeds via a two-step mechanism: the bond
to the leaving group breaks first before the a bond is formed.
The slow step is unimolecular, involving only the alkyl halide. It
exhibits first-order kinetics,
rate = k[(CH3),CCI]
■ E1 reactions also are regioselective and follow Zaitsev rule

14. Energy profile For E1 Reaction-

15. Reactivity of E1 reaction
In reactivity of E1 reaction reactivity decided by
formation of carbocation
1. The order of reactivity in E1 reaction is-
Tertiary carbocation > Secondary carbocation > Primary
carbocation
2. Tertiary carbocation is more active because it contains
more no.of electron rich group i.e methyl group which
donate electrons to carbocations and nullify its charge and
stabilize it

16. Orientation of E1 Reaction
■ Orientation of E1 reaction is also followed by saytzeff rule.
■ Saytzeff rule is says that hydrogen is lost from that carbon
which have lesser number of hydrogens.
■ Strong base prefer E2 reaction and weak base prefer E1
reaction.

17. The Zaitsev (Savtseff) Rule-
■ When alkyl halides have two or more different ẞ carbons, more
than one alkene product is formed.
In such cases, the major product is the more stable product-the
one with the more substituted double bond. This phenomenon
is called the “Zaitsev rule”.
■ The Zaitsev product or the more substituted alkene product is
more stable than the less substituted product. The stability of
the more substituted alkene is a result of number of different
contributing factors, including hyperconjugation.

18. Hoffman rule
■ According to this rule, major product is always least
substituted alkene i.e., major product is formed from
ẞ-carbon which has maximum number of hydrogen.
■ Ex

19. Referance-
1. Advanced Organic Chemistry Book by Arun Bahl and B.S Bahl.
2. Textbook of Organic chemistry by Morrison & Boyd 7th Edition.
3. Alkenes Elimination reactions by BCCCoaching Classes.