Kinds of ReactionsSN

Mechanisms (polar, non-polar)

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Organic reactions

Carbon skeleton

Functional group

Formation of alkyl groups

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ThemeOne Nucleophile is substituted for another nucleophile

General reaction

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A species that loves a nucleusSince nuclei are positively charged, so nucleophiles are negatively charged or bear a partial negative charge

Examples are lone pairs or a hydroxide ion.

Nucleophile is an electron rich species.

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An ion or molecule that is electron deficient and can accept electrons

Electrophiles are often reducing agents and Lewis acids

They are either positive ions (e.g. NO2 +) or

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molecules that have a positive charge on a particular atom(e.g. SO3, which has an electron-deficient sulphur atom)

In organic reactions they tend to attack negatively charged parts of a molecule

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Nucleophiles can be classified according to the kind of atom that forms a new covalent bond.1. Oxygen Nucleophile

(HO-, CH3O)

2. Nitrogen Nucleophiles (NH3,

RNH2…)

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3 Sulfur Nucleophiles (HS-, RS- …)

4 Halogen Nucleophiles (I-..)

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R – X is the general formula for organic halides.R = alkyl or aryl

X = F, Cl, Br & IMost of the organic halides are

creatures of the laboratory.Only few of them have been isolated

from natural products.

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Organohalogen compounds are important for several reason:

Versatile reagents in organic synthesis.

Can be converted into alkenes by dehydrohalogenation.

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As solvents (CH2Cl2, CHCl3)

Insecticides, herbicides, fire retardants.

Refrigerants and Polymers.

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ProticAproticPolarNon-Polar

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A solvent that is a Hydrogen-bond donor

The most common protic solvents contain –OH groups

WaterLow molecular weight alcoholsLow molecular weight carboxylic

acids

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A solvent that cannot serve as a hydrogen-bond

The most common aprotic solvents are:

DichloromethaneDiethyl etherDimethyl sulfoxide (DMSO)

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Ethyl bromide reacts with hydroxide ion to give ethanol.

OH- is the nucleophile.Bromide ion is called leaving group.

one new bond is formed

CH3 - CH2 - Br CH3 - CH2 - OH ++ Br-OH-

H2O

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If the nucleophile and substrate are neutral, the product will be positively charged.

If the nucleophile is a negative ion and substrate is neutral, the product will be neutral.

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The unshared pair of electron in the nucleophile can be used to make new covalent bond.

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:Nu + R:L R:Nu+ + :L-

:Nu- + R:L R:Nu + :L-

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In principle, these reactions may be

reversible.

Because the leaving group also has an

unshared pair of electron and that can be

used to make a new covalent bond.CH3 - CH2 - Br CH3 - CH2 - OH ++ Br-OH-

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We use various method to force the reaction to go in forward direction.1. Stronger nucleophile compared to the leaving group.2. large excess of one of the reagent3. Temperature

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There are some limitations:1. What kind of hybridized

carbon it is???2. What kind of nucleophile

it is???

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•No Nucleophilic Substitution will occur on the carbon which has double bond and triple bond in which leaving group is attached

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