Organic Chemistry

Types of Organic Reactions

Reactions happen all around us. Do you think there are types of organic reactions? Yes. When someone tries to study organic chemistry, the study of the types of organic reactions becomes an inherent part of such study module. Let us take a look at the types of organic reactions that scientists have been able to decipher until now.

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Types of Organic Reactions

There are five main types of organic reactions that can take place. They are as follows:

  • Substitution reactions
  • Elimination reactions
  • Addition reactions
  • Radical reactions
  • Oxidation-Reduction Reactions

Let us study each of these reactions in detail, to understand more about them.

organic reactions

(Source: wikihow)

1) Substitution Reactions

 In a substitution reaction, generally, one atom or a group of atoms take place of another atom or a group of atoms which leads to the formation of an altogether new substance. We can take an example of C – Cl bond, in which the carbon atom usually has a partial positive charge due to the presence of highly electronegative chlorine atoms.

In a nucleophilic substitution reaction, it is important that the nucleophile must have a pair of electrons and it also should have a high affinity for the electropositive species in comparison to the substituent which was originally present in the element. In order for the substitution reaction to occur, there are certain conditions that have to be present such as maintaining low temperatures same as room temperature.

Also, The strong base such as NaOH has to be in dilute form because suppose if the base is of higher concentration, there are chances of dehydrohalogenation taking place in the reaction. And, the solution needs to be in an aqueous state such as water for the reaction to take place. The types of Substitution reactions include nucleophilic substitution reactions and electrophilic substitution reactions.

2) Elimination Reactions

There are certain reactions which involve the elimination and removal of the adjacent atoms. After these multiple bonds are simultaneously formed and there is a release of small molecules as products as a result. One of the examples of a typical elimination reaction is the conversion of ethyl chloride to ethylene.

CH3CH2Cl       →         CH2= CH2      +        HCl

In the above reaction, the eliminated molecule is HCl, which can form out of the combination of  H+ from the carbon atom which is on the left side and Cl from the carbon atom which is on the right side.

3) Addition Reactions

An addition reaction is simply just the opposite of an elimination reaction. In an addition reaction, the components or molecules of A and B are added to the carbon-carbon multiple bonds and this is called an addition reaction. In the reaction given below when HCl is added to ethylene, it will give us ethylene chloride.

HCl      +     CH= CH2       →      CH3CH2Cl

4) Radical Reactions

Most of the organic reactions involve radicals and their movement. Addition of a halogen to a typically saturated hydrocarbon involves free radical mechanism. There are usually three stages involved in a radical reaction which are, initiation, propagation, and termination. Initially when the weak bond is broken initiation of the reaction takes place with the formation of free radicals. After that when the halogen is added to the hydrocarbon a radical is produced and finally, it gives alkyl halide.

A Solved Question for You

Q: In the context of an organic reaction, explain why such reactions take place.

Ans: In case of all organic reactions we can study that during a reaction, the solution will reach an equilibrium that favours the more stable side. In most cases, these will be reaction products as written from left to right, however, sometimes we must predict which side is favoured as in the case of acid-base reactions.

This can be demonstrated through DGº = – RT. In Keq = DH – TDS. If Keq > 1, in this case, the energy is released to the surroundings which are an exergonic reaction, the negative value of DGº, reaction favoured. If Keq, < 1, energy is absorbed from the surroundings which demonstrate an endergonic reaction, positive value of DGº, reaction not favoured.

Energy changes in a reaction can be illustrated by Energy Diagrams in which the highest energy point in a reaction step is called the transition state and the energy required to go from reactant to transition state is the activation energy. If a reaction occurs in more than one step, it must involve species that are neither the reactant nor the final product. Each step has its own free energy of activation.

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