ORGANIC REACTIONPrepace

What is Organic Chemistry?

It is defined as the study of hydrocarbons (compounds of hydrogen and carbon) and their derivatives

7 million Organic Compounds1.5 million Inorganic Compounds

Animal and plant matter, Foods, Pharmaceuticals, Cosmetics, Fertilizers, Plastics, Petrochemicals, Clothing

ORGANIC CHEMICALS ARE UNIVERSAL

OrganicChemicals

Biological matter• Plants• Animals• Microbes

Geological matter• Fossil Fuels

• Other

Atmosphericand

cosmic matter

Manufacturedproducts

Making a compound(SYNTHESIS)

ORGANIC REACTIONS

Nature give a lot of molecule

Drugs Dyes Rubber Cosmetics foods

.Limited Quantity

.Limited Variations

.Limited Activity

Organic ReactionIntroduction

Most molecules are at peace with themselves. Bottles of water, or acetone, or methyl iodide can be stored for years without any change in the chemical composition of the molecules inside.

When we add chemical reagents, say, HCl to water, sodium cyanide (NaCN) to acetone, or sodium hydroxide to methyl iodide, chemical reactions occur.

This chapter is an introduction to :

1. The reactivity of organic molecules (why

they don’t and why they do react)

2. How we can understand reactivity in

terms of charges and orbitals and the

movement of electrons

3. How we can represent the detailed

movement of electrons (the mechanism

of the reaction)

Molecules react because they move :• Whole molecules move continuously in space.• Bumping into each other, into the walls of the

vessel they are in, and into the solvent if they are in solution.

• When one bond in a single molecule stretches too much it may break and a chemical reaction occurs.

• When two molecules bump into each other, they may combine with the formation of a new bond, and a chemical reaction occurs.

Not all collisions between molecules lead to chemical change

Organic molecules

Many electrons at outer layer

All molecules repel each other

When will they react?

Reaction will occur only if the molecules are given enough energy (the activation energy for the reaction) for the molecules to pass the repulsion and get close enough to each other

Charge attraction brings molecules together

Cations (+) and anions (–) attract each other electrostatically and this may be enough for reaction to occur.

This inorganic style of attraction is rare in organic reactions. A more common cause of organic reactions is attraction between a charged reagent (cation or anion) and an organic compound that has a dipole.

Na + + Cl-

Polarity can arise from σ bonds too. The most electronegative element in the periodic table is fluorine and three fluorine atoms on electropositive boron produce a partially positively charged boron atom by σ bond polarization.

It is not even necessary for the reagent to be charged. Ammonia also reacts with acetone and this time it is the lone pair of electrons. That is attracted to the positive end of the carbonyl dipole.

Summarize• The presence of a dipole in a molecule represents an imbalance

in the distribution of the bonding electrons due to polarization of

a σ bond or a π bond or to a pair of electrons or an empty orbital

localized on one atom. • When two molecules with complementary dipoles collide and

together have the required activation energy to ensure that the

collision is sufficiently energetic to overcome the general

electronic repulsion, chemical change or reaction can occur.

Orbital overlap brings molecules togetherOther organic reactions take place between completely uncharged molecules with no dipole moments. The attraction between these molecules is not electrostatic. In fact, we know that reaction occurs because the bromine molecule has an empty orbital available to accept electrons. It is the antibonding orbital belonging to the Br–Br σ bond: the σ* orbital. There is therefore in this case an attractive interaction between a full orbital (the π bond) and an empty orbital (the σ* orbital of the Br–Br bond). The molecules are attracted to each other because this one interaction is between an empty and a full orbital and leads to bonding, unlike all the other repulsive interactions between filled orbitals.

Molecules repel each other because of their outer coatings of electrons. Molecules attract each other because of :• attraction of opposite charges • overlap of high-energy filled orbitals with low-energy empty orbitalsFor reaction, molecules must approach each other so that • they have enough energy to overcome the repulsion• the right orientation to use any attraction

ORGANIC REACTIONS CLASSIFICATIONS

BASED ON MECHANISM REACTIONS :

1. ADDITION : - ELECTROPHILIC

- NUCLEOPHILIC

- FREE RADICAL

2. ELIMINATION : - E1

- E2

3. SUBSTITUTION : - NUCLEOPHILIC (SN1, SN2)

- ELECTROPHILIC

4. REARRANGEMENT

BASED ON OXIDATION NUMBER CHANGE :

- ACID BASE

- REDOX

CLASSIFIED THIS REACTION

Cl

CH2

OH

NO2

H3C

O

NH-CH3

H2O

Br-Br

Br2

H2O

OH

Br

CH2-Br

NO2Br

H3C

O

OH

H2O

HCl

HBr

CH3-NH2

+

+

1.

2.

3. + +

4.+

+

5.

++

O OH