This presentation is about nucleophile and nucleophilicity and role of nucleophile in SN2 reaction.

1. NUCLEOPHILE
NUCLEOPHILICITY AND ROLE OF
NUCLEOPHILE IN SN2 REACTION

2. NUCLEOPHILE
 The term nucleophile is composed of two words
nucleo and –phile.the -phile suffix used in lot of
words mean lover of whatever comes in front.
 So the nucleophile is the lover of nucleus .
 Loving nuclei mean loving positive charges.So
the lover of positive charges must be negatively
charged.
 A nucleophile is an ion or molecule that donates
a pair of electron to form a new bond.
 The term nucleophile is used for a compound
that shares its lone pair with an atom other than
proton.
 Nucleophile has an unshared pair of electron
such as bromide and ammonia.

3. NUCLEOPHILE

4. NUCLEOPHILICITY
 Nucleophilicity is a measure how
readily nucleophile is able to attack on
electron deficient atom.
 In the case of SN2 reaction ,
ncleophilicity is a measure of how
readily the nucleophile attack on
carbon bonded to leavig
group.nucleophilicity refers the rate of
reaction of nucleophile with the carbon
at the reaction site.

5. NUCLEOPHILICITY
 Nucleophilicity is a kinetic
property.Many reactions of nucleophile
are not reversible.A bond forms , a
bond breaks and that the end of
reaction.The problem with This from a
measurement standpoint is that we
often cannot determine an equilibrium
constant for a reaction.And if we
cannot do that we cannot develop a
reactivity scale based on equilibria.

6. SN2 REACTIONS
 The abbreviation SN2 stands for nucleophilic
substitution , bimolecular.This type of
substitution reactions are bimolecular
because both the nucleophile and haloalkane
involve in rate determining step.
 This is the second order reaction .Doubling
the concentration of alkyl halide doubles the
rate of reaction.Doubling the concentration of
nucleophile doubles the rate of
reaction.Doubling the concentration of both
nucleophile and alkyl halide quadruples the
rate of reaction.
 Rate =k [A][B]

7. SN2 REACTION

8. Strength of the nucleophile
 A stronger nucleophile is an ion or molecule
that reacts faster in SN2 reaction then a
weaker nucleophile under the same
condition.A strong nucleophile is much more
effective than weak one in attacking at
electrophilic carbon atom.
 Both methanol and methoxide ion have easily
shared pairs of non-bonding electrons.But
methoxide reacts with eclectrophile in the
SN2 reaction about 1 million times faster than
methanol.It is a generally true that a specie
with a negative charge is stronger
nucleophile than a smilar neutral specie.

9. STRENGTH OF
NUCLEOPHILE

10. SOLVATION EFFECTS ON
NUCLEOPHILICITIES
The solvent in which nucleophilic substitution reactions
are carried out has a marked effect on nucleophilicities.
 In polar aprotic solvents , Anoins are only weakly
solvated and therefore free to participate in nucleophilic
substitution reaction and basicity dictates
nucleophilicity.
 In polar protic solvents , anoins are highly solvated by
hydrogen bonding with solvent molecules and therefore
are less free to participate in nucleophilic substitution
reactions and polarizeability dictates nucleophilicity.
 So iodide is more polarizabile than other halides. so in
polar protic solvents , it is a strong nucleophile.
 POLRAR APROTIC
iodide>bromide>chloride>flouride
POLAR PROTIC
flouride<chloride<bromide<iodide

11. NUCLEOPHILICITY IS
AFFECTED BY STERIC
AFFECTS The nucleophile attacks from the back side of
carbon-leaving group bond.As the leaving
group departs with electron pair. The
nucleophile supplies another electron pair to
crbon.
 So nucleophilicity is affected by steric affects
because a bulky nucleophile cannot
approach the back side of carbon so easily
as a less sterically hindered nucleophile can.
 Therefor tertiary butoxide with its three
methyl groups is a poorer nucleophile than
ethoxide ion even though tertiary butoxide ion
is stronger base than ethoxide ion.

12. NUCLEOPHILICITY IS
AFFECTED BY STERIC
AFFECTS