HOW ORGANIC REACTIONS OCCUR- MECHANISM

In this article we are going to discuss about the kinds of reactions in organic chemistry and how they occur theoretically.
Organic chemistry often seems like a strange collection of facts, a collection of millions of compounds, dozens of functional groups and a seemingly endless number of reactions.

Far from being a collection of isolated facts, organic chemistry is a beautiful logical subject unified by a few broad themes. When these themes are understood,learning organic chemistry becomes much easier and rote memorization can be avoided. The aim of this write up is to point out the themes and to clarify the patterns that unify organic chemistry. So we'll be discussing about about the fundamental kinds of organic reactions that can take place and also how they can be described.

KINDS OF ORGANIC REACTIONS

Organic reactions can be classified in two ways namely;

• By what kind of reactions occur, and
• By how reactions occur.

To study this aspect of organic chemistry, we must discuss in details the kinds of reactions that can take place.

There are four fundamental kinds of organic reactions namely;

• Addition Reactions: this kind of Reactions occur when two reactants are added together to form a single new product with no atoms "left over." This process can be expressed generally as;  A + B ------- C                                                           Taken an important addition reaction of ethene reacting with acids such as HBr (hydrogenbromide) to yield alkyl halides: .                    

• Elimination Reactions: this kinds of Reactions are opposite of addition Reactions. Elimination reaction occurs when a single reactant spits apart into two products, a process we can generalize as; .    A _______ B + C.                     Example of an important elimination reaction, alkyl halides such as bromoethane split apart into an acid and an alkenewhen treated with base: .                                                           

• Substitution Reactions: this takes place when two reactants exchange parts to give two new products, this process can be generalize as;.           A--B + C--D _____ A--C + B--D
• A good example of a substitution   reaction, alkanes such as methane react with chlorine gas in the presence of   ultraviolet light to yield alkyl halides. A--Cl   group from chlorine replaces (substitutes   for) the -H group of methane, and two new   products result: .      

• Rearrangement Reaction: this kind of reaction occurs when a single reactant undergoes a reorganization of bonds and atoms to yield a single isomeric product, this process can be generalize as;  A ____ B .  Example of a rearrangement Reaction, the alkene 1- butene can be converted into it's constitutional isomer, 2- butene, by treatment with an acid catalyst:

               

                         

HOW ORGANIC REACTIONS OCCUR: MECHANISM

Having looked at the kinds of Reactions that occurs in organic chemistry, we want to discuss how this reactions occur. An overall description of how a specific reaction occurs is called a reaction mechanism.


A mechanism helps us to understand what exactly takes place at each stage of a chemical transformation. It describes which bonds are broken and in what order, which bonds are formed and in what order, and the rates of each step. A complete mechanism should also account for all reactants used, all product formed and the amounts of each.

All chemical reactions involve bond breaking and bond formation. When two reactants come together, react, and yield products, specific chemical bonds in the starting materials are broken and specific chemical bonds are formed.  Fundamentally there are only two ways this process can take place namely; HOMOLYTIC and HETEROLYTIC cleavage. i.e HOMOLYTIC bond breaking and making.

NOTE: Polar processes are the more commonly encountered reaction type in organic chemistry.

In addition to polar reactions, we also have radical reactions and pericyclic reactions.

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