Organic Reactions Types, Mechanisms

You may have learnt lot of organic reaction in organic chemistry. For some reactions, a mechanism is given to explain the reaction process like why this reaction happens and how the reaction occurs until give final products.

Organic reactions are categorized into 4 sections according to the reaction happens because different reactions happen in different mechanisms. That four types are listed below.

Mechanism of addition of HBr molecule to ethene molecule. It is a two step reaction.

After you studied this lesson completely, see your organic reactions and mechanisms lessons to understand furthermore about organic reactions types.

Types of organic reactions

Organic reagents are categorized into 4 sections according to their mechanisms of reactions.

1. Addition reactions
2. Substitute reactions
3. Elimination reaction
4. Rearranging reactions

Addition reactions

Adding atoms or groups through double or triple bonds are defined as addition reactions. But any groups existed earlier before the reaction in the molecule are not removed. Only new groups are added.

Examples of Addition reactions

1. Catalyst hydrogenization of alkenes and alkynes
2. Brominization of alkenes and alkynes
3. Halogen acids (H-X) addition to alkenes and alkynes
4. Grignard reagent and aldehyde, ketone reaction

Addition reactions mechanisms also can be categorized to different kinds.

1. Electrophilic Addition
2. Nucleophilic Addition
3. Free-Radical Addition

Electrophilic addition reactions

1. As the first step in this mechanism, a positive species approaches the double or triple bond and in the first step forms a bond by donation of the p pair of electrons to the electrophilic species to form a σ pair:
2. In the second step, first step product combines with a species carrying an electron pair and often bearing a negative charge. This specie may be a one generated at first step. See the figure of bromination mechanism.

Example reactions of electrophilic adddition reactions are given below

• Addition of bromine liquid to alkenes. Two bromine molecules are added to alkene molecule to give produce alkyl halide compound.

Nucleophilic addition reaction

A negatively charged species attacks the positively charged carbon atom in first step and forms a new bond between that carbon atom and negatively charged species.

Some example reactions are given below for nucleophilic addition reaction.

• Grignard reagent reaction with aldehyde or ketone or acid chloride or ester.

Substitution reactions

Substitution reactions is defined as replacing one atom or group instead of another atom or group (substituting). Substitution reactions also can be categorized as below.

1. Electrophilic substitution reactions
2. Nucleophilic substitution reactions
3. Free Radicals substitution reactions

Examples of substitution reactions

1. Alkyl halides and dilute aqueous alkali reaction
2. Alcohols and HBr reaction
3. Benzene and concentrated sulfuric acid and concentrated nitric acid reaction to prepare nitrobenzene

Rearranging reactions

Atoms or groups are not added or not removed. Only structure of bonds is changed and it gives new compounds.

Examples of rearranging reactions

1. Hoffmann's degradation