SN Reaction REVIEW!

What the heck is SN reaction?

• SN reaction stands for NUCLEOPHILIC • SUBSTITUTION reaction

• Substitution… so, something re-places

something…AB + C AC + B

• There are two types of Sn reac-tion:- Sn2 and Sn1

Before we discuss SN2 reaction…

• There are two main characters in this reactions

Alkyl Halide and Nucleophile

Alkyl Halide

A compound that contains carbon and hydrogen (carbohydrates) as well as

the halogens (Cl, Br, I) as a leaving group

SN 2 reaction!!• 1 step mechanism

AB + C AC + B

A= Alkyl halideB= Leaving groupC= Nucleophile

C attacks A, and B leaves A at the same time!!

Why do we call it SN2 then???

The rate (how easy the reaction goes) involves concentration of two characters

Alkyl Halide and Nucleophile

More Alkyl Halide, faster the reaction

More Nucleophile, faster the reac-tion

We call this Bimolecular reac-tion

SN1 Reaction!It is a 2 step reaction!

AB + C A + B + C AC+B

Leaving group B leaves A, THEN C attacks A

Mechanism of SN1 Reaction

Again, Why do we call it SN1 if there are 2 steps??

• The rate of SN1 reaction only in-volves the concentration of alkyl halide.

SN1 reaction = How fast the leav-ing group leaves and forms a carbo-cation?More Alkyl Halides = Faster reac-

tionMore nucleophile = NOTHING HAP-PENS

Unimolecular Reac-tion

Nucleophile

Oh, bye the way, good leaving groups are weak baseI>Br>Cl>>F

Nucleophile steals leaving group’s spot

Nucleophilicity is a kinetic property.Faster, the better.L.G. property depends on basicity (weak base, better L.G.)

How do you know which one is good nucleophile?

Negative Charge

What does it mean, nucle-ophile?

Nucleo:Nux – nutNucleus – kernel, core

Phile:Philia – love, affection

Molecule is satisfied when all atoms have octet (except hy-drogen) and 0 formal charge. If they don’t have this, they will find someone to share love.

Nuc. increase to the left of periodic table

This is same with basicity. many good nucleophiles are good base. EXCEPT:

I-, Br-, Cl-, N3-, HS-,

CH3CO2-

B E

AR A

Solvent Effect and nucleophilicity

F-I-

OH

H

OH

H

O

H

H

O H

H

O

H

H

O

H

H

O H

H

O

H

H

How come it is not same as basicity???

Although nonpolar solvent make Sn2 favors, we need to use polar aprotic (DMF, DMSO),Because they have high BP, and cannot be separated by liquid-liquid extraction

Solvent for Sn1

Polar protic is favore, because it stabilize carbocation inter-mediates.

Competitive reaction