To understand the reactions mechanisms the basic must be clear.
We begin by defining some basic terms that will be used
frequently as this subject is elaborated. Chemical Reaction: A transformation resulting in a change of composition, constitution and/or configuration of a compound.
Reactant or Substrate: The organic compound undergoing
change in a chemical reaction. Other compounds may also be
involved, and common reactive partners (reagents) may be identified.
The reactant is often (but not always) the larger and more complex
molecule in the reacting system. Most (or all) of the reactant molecule
is normally incorporated as part of the product molecule.
Reagent: A common partner of the reactant in many chemical
reactions. It may be organic or inorganic; small or large; gas, liquid
or solid. The portion of a reagent that ends up being incorporated in
the product may range from all to very little or none.
Product(s): The final form taken by the major reactant(s) of a
reaction.
Reaction Conditions: The environmental conditions, such as
temperature, pressure, catalysts & solvent, under which a reaction progresses optimally. Catalysts are substances that accelerate the rate
( velocity) of a chemical reaction without themselves being consumed
or appearing as part of the reaction product. Catalysts do not change
equilibrium positions.
Chemical reactions are commonly written as equations:
Reactant(s) + Reagent(s) -----------> Product(s)
(Depending upon reaction conditions)
CLASSIFYING ORGANIC CHEMICAL REACTIONS
These are the "tools" of a chemist, and to use these tools
effectively, we must organize them in a sensible manner and look
for patterns of reactivity that permit us make plausible predictions.
Most of these reactions occur at special sites of reactivity known as
functional groups, and these constitute one organizational scheme
that helps us catalog and remember reactions. This is best
accomplished by perceiving the reaction pathway or mechanism of
a reaction.
CLASSIFICATION BY STRUCTURAL CHANGE
First, we identify four broad classes of reactions based solely
on the structural change occurring in the reactant molecules. This
classification does not require knowledge or speculation concerning
reaction paths or mechanisms.
The letter R in the following illustrations is widely used as a
symbol for a generic group. It may stand for simple substituents such
as H-or CH3-,or for complex groups composed of many atoms of
carbon and other elements.
Types of Organic Reactions
1. Organic compounds undergo four main types of reaction, namely addition, substitution, elimination and rearrangement.
(a) Addition reaction
(c) Elimination reaction
(d) Rearrangement
We begin by defining some basic terms that will be used
frequently as this subject is elaborated. Chemical Reaction: A transformation resulting in a change of composition, constitution and/or configuration of a compound.
Reactant or Substrate: The organic compound undergoing
change in a chemical reaction. Other compounds may also be
involved, and common reactive partners (reagents) may be identified.
The reactant is often (but not always) the larger and more complex
molecule in the reacting system. Most (or all) of the reactant molecule
is normally incorporated as part of the product molecule.
Reagent: A common partner of the reactant in many chemical
reactions. It may be organic or inorganic; small or large; gas, liquid
or solid. The portion of a reagent that ends up being incorporated in
the product may range from all to very little or none.
Product(s): The final form taken by the major reactant(s) of a
reaction.
Reaction Conditions: The environmental conditions, such as
temperature, pressure, catalysts & solvent, under which a reaction progresses optimally. Catalysts are substances that accelerate the rate
( velocity) of a chemical reaction without themselves being consumed
or appearing as part of the reaction product. Catalysts do not change
equilibrium positions.
Chemical reactions are commonly written as equations:
Reactant(s) + Reagent(s) -----------> Product(s)
(Depending upon reaction conditions)
CLASSIFYING ORGANIC CHEMICAL REACTIONS
These are the "tools" of a chemist, and to use these tools
effectively, we must organize them in a sensible manner and look
for patterns of reactivity that permit us make plausible predictions.
Most of these reactions occur at special sites of reactivity known as
functional groups, and these constitute one organizational scheme
that helps us catalog and remember reactions. This is best
accomplished by perceiving the reaction pathway or mechanism of
a reaction.
CLASSIFICATION BY STRUCTURAL CHANGE
First, we identify four broad classes of reactions based solely
on the structural change occurring in the reactant molecules. This
classification does not require knowledge or speculation concerning
reaction paths or mechanisms.
The letter R in the following illustrations is widely used as a
symbol for a generic group. It may stand for simple substituents such
as H-or CH3-,or for complex groups composed of many atoms of
carbon and other elements.
Types of Organic Reactions
(a) Addition reaction
- Occurs when two reactants react to form one product.
- Involves compounds with multiple bonds (unsaturated). The reaction results in breaking of one pi (π) bond to form two sigma (σ) bonds.
(b) Substitution reaction
- Involves replacing one atom or group with another.
(c) Elimination reaction
- Involves the elimination of two neighboring atoms from saturated molecules, with the formation of multiple bonds.
- The reverse of addition reaction.
(d) Rearrangement
- Occurs at the transition stage of a reaction involving carbocation.
- Occurs when a single reactant reorganizes the bonds or atoms.
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