Types Of Organic Reactions

Organic reactions are chemical processes in which organic substances are involved. Addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions, and redox reactions are the fundamental organic chemistry reaction types. Organic reactions are utilized in the production of new organic compounds in organic synthesis. Many man-made compounds, such as pharmaceuticals, plastics, food additives, and textiles, rely on organic interactions.

There is no limit to the number of organic reactions and processes that can occur. However, certain broad patterns emerge that may be used to characterize a wide range of frequent or beneficial reactions. Each reaction has a stepwise reaction mechanism that describes how it occurs, albeit this full explanation of stages is not always obvious from a list of reactants alone. Organic reactions can be classified into various categories. Some responses are classified as belonging to more than one type. For example, some substitution processes follow an addition-elimination route.

Organic reactions are chemical processes that involve organic compounds. Several of these reactions have functional group correlations. An organic reaction mechanism is a thorough, step-by-step description of how an organic compound reaction happens. Organic chemistry is important because it investigates life and all of the chemical processes connected with life. These reactions are crucial in the production of numerous chemicals that play an active part in living organisms.

Mechanisms of Organic Reactions: Fundamental Concepts

• A reaction mechanism is a broad description of how a reaction occurs.
• A mechanism specifies how and in what order bindings are broken, as well as which bonds form and in what order at each stage of a chemical process.
• It provides a detailed explanation of how electrons travel during chemical reactions.
• A reaction mechanism must account for all reactants and products generated.

Substitution Reactions

A substitution reaction is the direct replacement (displacement or substitution) of an atom or group of atoms in an organic molecule by another atom or group of atoms with no change to the remaining part of the molecule. The product of the substitution is known as the substitution product, and the additional atom or group of atoms that enter the molecule is known as the substituent.

Substitution Reactions and Their Types:

Substitution reactions are further classified into three types based on the nature of the attacking reagent: electrophilic, nucleophilic, and free radical.

Nucleophilic Substitution Reactions

The substitution reaction is known as a nucleophilic substitution reaction when the attacking reagent is a nucleophile (Nu– or Z–). These are mainly alkyl halide reactions.

For instance, an alkyl halide can be hydrolyzed using an aqueous base.

Nucleophilic substitution reactions are classified into two types: They’re

1. SN2 (Substitution, nucleophilic, bimolecular)
2. SN1 (Substitution, nucleophilic, unimolecular)

1. The SN2 Reaction or Mechanism

The SN2 mechanism is a one-step process with no intermediates. The nucleophile hits the substrate from the opposite (rear) side to the leaving group in this reaction.

The hydrolysis of methyl bromide in the presence of NaOH is a classic example of this process.

2. The SN1 Reaction or Mechanism

The SN1 reaction occurs in two steps. The first stage is gradual ionization, which results in the formation of a carbocation. The nucleophile then attacks the carbocation quickly in the second stage.

R-X→R++X-; rate-determining step

R++Nu-→R-Nu; very fast attack

The carbocation is a powerful electrophile that interacts quickly with both strong and weak nucleophiles.

The following elements influence the SN1 reaction:

1. The influence of the substrate structure
2. The effect of the leaving group
3. The effect of substitution
4. The effect of the attacking nucleophile

Electrophilic Substitution Reactions

The attacking reagent in these reactions is an electrophile. These are common reactions for arenes and other aromatic compounds. Halogenation, nitration, sulphonation, and Friedel-Crafts reactions are examples.

Free Radical Substitution Reaction

In free radical substitution reactions, the attacking reagent is a free radical. These reactions occur in the presence of UV light or at high temperatures. For example, the Chlorination of methane produces chloromethane.

Addition Reaction

Addition reactions occur when two reactive molecules combine to generate a single product molecule. Such reactions are prone to compounds with a high number of (double and triple) bonds.

Based on the characteristics of the invading species, addition reactions are divided into three groups. They are classified as electrophiles, nucleophiles, or free radicals.

1. Electrophilic Addition Reaction

Electrophilic addition reactions are electrophilic addition processes caused by electrophiles. This is a common alkene and alkyne reaction. An electrophilic mechanism, for example, is used in the addition of halogen acids to alkenes.

2. Nucleophilic Addition Reaction

Nucleophilic addition reactions are those induced by nucleophiles. This is a common aldehyde and ketone reaction. For example, the base-catalyzed addition of HCN to aldehydes or ketones.

3. Free Radical Addition Reaction

Inorganic chemistry, free-radical addition is an additional process that incorporates free radicals. The addition might happen between two radicals or between a radical and a non-radical.

Elimination Reactions

The elimination reaction occurs when two atoms or groups, either from neighboring places or from the same position, are eliminated or removed, resulting in the creation of multiple bonds (i.e., a double or triple bond). There are two kinds of reactions. They do;

1. β-Elimination processes: In these reactions, two atoms or groups are lost from the molecule’s neighboring carbon atoms. As an example, When alcohols are heated in the presence of strong sulphuric acid, they dehydrate and release water
2. α-Elimination reactions: In these reactions, two atoms or groups from the same carbon atom in the molecule are lost or eliminated. For example; Dehydrogenation of primary or secondary alcohols using reduced copper at 573k.

Rearrangement Reactions

Rearrangement reactions include the movement of an atom or a group from one atom to another inside the same molecule. A rearrangement reaction example is the Wohler synthesis of urea from ammonium cyanate.

Polymerization Reactions

In nature, polymerization is a basic addition reaction. It is a process in which a large number of identical or dissimilar molecules of unsaturated chemicals unite to generate a larger molecule with a greater molecular mass.

Pericyclic Reactions

Ionic or free radical intermediates are not used in many chemical processes. These reactions, on the other hand, take place in a single step by the use of a cyclic transition state. In these processes, bond creation and bond breakdown occur concurrently. These reactions do not require a catalyst and can be triggered by either heat or light.

• Isomerization Reactions

Isomerization processes include the interconversion of one isomer into another while maintaining the molecular formulas and carbon skeletons of the reactant and product intact. For example; At 575 degrees Celsius, 1-bromobutane isomerizes to 2-bromobutane in the presence of anhydrous AlCl₃.

• Condensation Reactions

Two or more molecules of the same or different reactants combine to generate a product, with or without the removal of simple molecules likeH₂O, HCl, NH₃, ROH, and so on. In the presence of dilute alkali, for example, two molecules of acetaldehyde condense to create -hydroxybutanal.

Also read: Electronic displacements in a covalent bond

FAQs

How do you determine whether a reaction is endothermic or exothermic?

Chemical processes that release energy are referred to as exothermic reactions, whereas reactions that absorb energy are referred to as endothermic reactions.

Why are organic reactions so slow?

Organic substances are molecules that have strong covalent bonds. Because these molecules have such strong interactions, it is more difficult for them to react; consequently, it takes a long time.

Q. How do you categorize different types of reactions?

Ans: Reactions are categorized as:

1. synthesis reactions
2. decomposition reactions
3. single displacement reaction
4. double displacement reaction
5. Combustion reaction