E1 Elimination reaction

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,1 st Sem Guided by- Dr. Tamanna Narsinghani Mam Professor, DAVV Subject-Advance organic chemistry Code-MPC-102T Seminar presentation T opic- 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 , T here 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.

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