Types of Organic Reactions

Seven types of Organic reactions exist. They are:

1. Substitution reaction

• Nucleophilic reaction
• Electrophilic reaction
• The free radical substitution reaction

2. Addition reaction

• Electrophilic reaction
• Nucleophilic reaction

3. Elimination reaction
4. Rearrangement reaction
5. Condensation reaction
6. Pericyclic reaction
7. Polymerisation reaction

Substitution Reactions

Substitution reaction, also known as displacement reactions, occurs when another functional group replaces one functional group of a chemical compound. Organic chemistry relies heavily on substitution reactions. Organic chemistry substitution reactions can be classified as either nucleophilic or electrophilic depending on the type of reagent used. The halogenation reaction is a good illustration of a substitution reaction. After exposure to irradiation, some of the chlorine gas (Cl-Cl) molecules’ electrons (Cl.) become highly nucleophilic. There are two of them, one of which breaks into an unstable covalent bond and takes the freed proton to form H-Cl. CH₃Cl is formed by a covalent bond between the CH₃ radical and Cl radical.

Nucleophilic Substitution Reaction

There are many different types of reactions classified as “nucleophilic substitutions,” which are reactions where one nucleophile replaces a weaker nucleophile,which leaves and is called a leaving group. The substrate consists of the entire molecular unit of the electrophile and the leaving group. According to this reaction, the substrate R-LG can be depicted as follows: Nuc: + R-LG → R-Nuc + LG: The nucleophile’s electron pair (:) attacks the substrate (R-LG), forming a new covalent bond as it does so (Nuc-R-LG). When the leaving group (LG) leaves with an electron pair, the previous state of charge is restored. R-Nuc is the primary product here. The nucleophile is negatively charged or neutral, while the substrate is positively charged or neutral. Hydrolysis of an alkyl bromide (R-Br) using OH as the attacking nucleophile and Br as the group leaving is an excellent example of a nucleophilic substitution reaction. R-Br + OH+ R-OH + OH+

Electrophilic Substitution Reactions

The most famous electrophilic substitution is electrophilic aromatic substitution. For the most part, electrophilic aromatic substitution reactions require the involvement of electrophiles. Electrophile E+ attacks the electron resonance arrangement of the benzene ring. A carbocation resonating structure is formed when the resonating bond is broken. An aromatic compound is synthesised after a proton is removed from the ring.

Free Radical Substitution Reaction

Substitution Reactions involving radicals are called “radical substitution reactions.” The Hunsdiecker reaction is an example of a substitution reaction involving organometallic compounds. For example, an organometallic compound (RM) is linked to an organic halide (RX) in this type of reaction, resulting in a new carbon-carbon link between the two compounds when they react. Ullmann reactions can be found in some instances. Also halogenation in presence of light is a free radical substitution reaction.

Addition Reaction

Inorganic chemistry’s addition reaction can be explained by two or more molecules combining to form a larger one. Only a few chemical compounds, such as those with triple bonds (alkynes), carbon-carbon, double bonds (alkenes), or imine (C=N) groups, are capable of addition reactions. Carbonyl (C=O) groups, which have a carbonyl (C=O) double bond, can also be added to other molecule types.

Electrophilic Addition Reactions

It is possible to create two new sigmas () bonds by destroying a pi () bond in an electrophilic addition reaction in inorganic chemistry. A double or triple bond is required for the electrophilic addition reaction substrate. When an electrophile X+ forms a covalent bond with an electron-rich unsaturated C=C double bond, this reaction occurs. A carbocation is formed when the positive charge on X is transferred to the carbon-carbon bond. Step 2 of an electrophilic addition reaction sees an anion (Y) combine with the positively charged species (P) to form the second covalent bond. Region selectivity is critical in every asymmetric carbon addition reaction, and Markovnikov’s law is often used to determine it. Anti-Markovnikov addition reactions always occur with organoborane compounds. Instead of an addition reaction, when an electrophilic attack is made on an aromatic system, electrophilic aromatic substitution occurs.

Nucleophilic Addition Reactions

An electrophile with an electrophilic double, triple, or pie ( bonds) can add two additional single sigma bonds to produce a new carbon centre. Many different nucleophiles can be added to carbon-heteroatom double or triple bonds, such as -CN or>C=O. The carbon atoms in these polar bonds carry a slight positive charge due to the large difference in electronegativity between the two atoms. This produces an electrophile molecule and the carbon atom with the electrophilic centre, which is the nucleophile’s primary target. 1,2 nucleophilic addition is another name for this type of reaction.

Elimination Reaction

Two substituents are ejected from a molecule in one or two steps during these reactions. The “E2 reaction” refers to the one-step mechanism, while the “E1 reaction” refers to the two-step mechanism. The numbers have nothing to do with the mechanism’s number of steps, regardless of whether the reaction is bimolecular or unimolecular in its kinetics. The E1CB reaction occurs when a molecule can form an anion but lacks a good leaving group. Finally, an “internal” removal mechanism known as the Ei mechanism completes the pyrolysis of xanthate and acetate ester esters. The E2 reaction involves anti-periplanar atoms leaving. E1 involves the creation of a carbocation that can be rearranged and E1CB involved formation of an anion. They all follow different mechanisms but have the same end result of a group of atoms leaving and a double bond being left behind in the substrate.

Rearrangement Reaction

The carbon frames of a molecule are rearranged to give a structural isomer of the original molecule in a comprehensive class of organic reactions. Substituted atoms frequently swap places in the same molecule. Also, intermolecular reorganisation is a part of the process. Simple and distinct electron transfers do not adequately describe a rearrangement (represented by curly arrows in organic chemistry textbooks). As in Wagner-Meerwein reorganisation, the real process of alkyl groups passing may involve fluidly shifting the alkyl group along with a bond, rather than ionic bond-breaking and making. There are ways to simulate a rearrangement reaction using the curved arrows for a series of discrete electron transfers, but these are not essentially realistic. There are multiple rearrangement reactions that take place in organic chemistry.

Condensation Reaction

Classification of organic reactions is based on chemical reactions that sequentially produce the addition product and water molecules (later named condensation). It is possible to include functional groups and ammonia, acetic acid, and ethanol in the reaction to avoid this. An acidic or basic environment, or even a catalyst, can be used as a catalyst for these reactions. This reaction class is required to form peptide bonds between amino acids and the biosynthesis of fatty acids. Several types of condensation reactions are possible. The aldol condensation, the Knoevenagel condensation, the Claisen condensation, and the Dieckman condensation are all examples of aldehyde condensation reactions (intramolecular Claisen condensation).

Pericyclic Reaction

One of the most common organic reactions involves a cyclic transition state, and it proceeds in a coordinated fashion.

Polymerisation Reaction

It combines monomer molecules to form polymer chains or 3-D three-dimensional networks through a chemical reaction in polymer chemistry. It is possible to categorise polymerisation in a variety of ways. Polymerisation is an example of alkene polymerisation in which each styrene monomer has its double bond replaced by one bond and one other bond to another styrene monomer. It requires a catalyst and is highly useful in polymer chemistry.

Conclusion

Different types of organic reactions were the subject of discussion in this chapter. Organic chemistry relies heavily on organic reactions. They need to be studied in depth in order to gain a better understanding of organic chemistry. We can learn more about organic reactions by studying the various mechanisms discussed here. Using a chemical equation, you can convey a great deal of information in a small amount of space. We now know that matter is made up of atoms.Almost all organic reactions fall into one of the categories we have discussed above.