Types of Organic Reactions

Organic Chemistry Reactions list

There is a total of eight types of Organic reaction

  • 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. Polymerization reaction
  • 1. Substitution reaction

  • Substitution reaction or displacement reaction is a chemical reaction in which one functional group in a chemical compound is substituted by another functional group. Substitution reactions are very important in organic chemistry. Substitution reactions in organic chemistry are categorized either as nucleophilic or electrophilic depending upon the reagent that are involved.

    Halogenation is a good example of a substitution reaction. When chlorine gas (Cl-Cl) is irradiated, some of the molecules are divided into two chlorine radicals (Cl.) whose free electrons are highly nucleophilic. One of them break into a weak C-H covalent bond and takes the liberated proton to form the electrically neutral H-Cl. The other radical changes to covalent bond with the CH3· to form CH3Cl (methyl chloride).

    Nucleophilic substitution

    Inorganic and inorganic chemistry, nucleophilic substitution is an important class of reactions where a nucleophile selectively bonds and replaces a weaker nucleophile which then turns into a leaving group; The remaining positive or partly positive atom becomes an electrophile. The whole molecular unit of electrophile and the leaving group form the part known as the substrate.

    The most common form for the reaction can be given as follows, where R-LG shows the substrate.
    Nuc: + R-LG → R-Nuc + LG:

    The electron pair (:) from the nucleophile attacks the substrate (R-LG) creating a new covalent bond (Nuc-R-LG). The previous state of charge is restored when the leaving group (LG) leaves with an electron pair. The main product, in this case, is R-Nuc. In such reactions, the nucleophile is typically electrically negatively charged or neutral, while the substrate is usually positively charged or neutral.

    A perfect example of nucleophilic substitution reaction is the “hydrolysis of an alkyl bromide’, R-Br, under basic conditions, where the attacking nucleophile is the OH− (base) and the group leaving is Br−
    R-Br + OH → R-OH + Br

    Electrophilic substitution reactions

    Electrophiles are involved in electrophilic substitution reactions, mainly in electrophilic aromatic substitutions reaction.

    In this example below, the benzene ring's electron resonance arrangement is attacked by an electrophile E+. The resonating bond is destroyed and a carbocation resonating structure form. Finally, a proton is removed out and a new aromatic compound is made

    Radical substitution reaction

    A radical substitution reaction is a reaction which contains radicals.
    An instance is the Hunsdiecker reaction:

    Organometallic Substitution reaction

    This type of reaction belongs to a class of metal-catalyzed reactions linking an organometallic compound RM and an organic halide R'X that combine together and react to produce a compound of the type R-R' with the development of a new carbon-carbon bond. Instances contain Ullmann reaction.

  • 2. Addition reaction

  • An addition reaction, inorganic chemistry, can be explained in simple terms where two or more molecules combine together to produce a larger one.

    These reactions are bounded to few chemical compounds that have several bonds, such as molecules with triple bonds (alkynes)carbon-carbon, double bonds(alkenes), or imine (C=N) groups, can undergo addition reaction. Molecules containing carbon—hetero double bonds like carbonyl (C=O) groups, as they too have double-bond property can also undergo addition reaction.

    There are two key types 

    Electrophilic Addition

    Inorganic chemistry, an electrophilic addition reaction is a reaction in which, a pi (π) bond is destroyed and two new sigmas (σ) bonds are produced. The electrophilic addition reaction substrate needs to have a double bond or triple bond.

    The driving force for this reaction is the creation of an electrophile X+ that create a covalent bond with an electron-rich unsaturated C=C double bond. The positive charge on X is shifted to the carbon-carbon bond, forming a carbocation during the production of the C-X bond.

    In step 2 of an electrophilic addition reaction, the positively charged species in-between combines with (Y) that is electron-rich and generally an anion to produce the second covalent bond.

    Step 2 is the same nucleophilic attack process which can be seen in an SN1 reaction. The similar nature of the electrophile and the nature of the positively charged intermediate are not constantly clear and it depends on reactants and reaction surroundings.

    In every asymmetric addition reaction to carbon, region selectivity is significant, and it is often determined by Markovnikov's law. Organoborane compounds always give anti-Markovnikov additions reaction. Electrophilic attack to an aromatic system will result in electrophilic aromatic substitution reaction rather than an addition reaction.

    In Electrophilic addition reaction, the electrophile which is containing positive charge will affect the development of the total structure, which thus stands a positive charge as well, to make up for the new addition reaction, which later results in the intermediate, having that positive charge. This intermediate is important for understanding the electrophilic addition reaction, which is due to the positive nature of the particles are involved. If this is done, now the reactions can be understood by these additions as positively charged addition reactions. The positive charge allows resultant as the intermediate form otherwise called the total structure of such an intermediate. The end creation, therefore, has the complete structure, with the addition of Y, a nucleophile.

    Nucleophilic addition reactions

    Nucleophilic addition reactions where, nucleophiles with an electrophilic double, triple bond or pie (π bonds) produce a new carbon center with two additional single, or sigma σ, bonds. Addition of a nucleophile to carbon-heteroatom double or triple bonds like -C≡N or>C=O display great variety. These kinds of bonds are polar and have a big difference in their electronegativity among the two atoms; therefore, their carbon atoms transport a slightly positive charge. This creates the molecule of an electrophile and the carbon atom with the electrophilic center; this atom is the prime target for the nucleophile.

    This kind of reaction is also known as 1,2 nucleophilic addition. 

  • 3. Elimination reaction

  • In these reactions, two substituents are thrown out from a molecule in any one or two-step mechanism. The one-step mechanism is called the "E2 reaction", and the two-step mechanism is called the "E1 reaction". The numbers do not have to do anything with the number of steps in the mechanism, however bimolecular and unimolecular the kinetics of the reaction separately. In cases where the molecule is able to form an anion but has a poor leaving group, the third kind of reaction, E1CB, occurs. Eventually, the pyrolysis of xanthate and acetate esters proceeds through an "internal" removal mechanism, known as the Ei mechanism.

    Sir Christopher Ingold proposed a model to explain a particular type of chemical reaction during the 1920s: the E2 mechanism. Where E2 stands for bimolecular elimination. The reaction contains a one-step mechanism in which carbon-hydrogen (C-H) and carbon-halogen (C-X) bonds breakdown to procedure a double bond (C=C Pi bond)

    • E2 is one step elimination process, with a one transition state.
    • The reaction rate is in second order because it's influenced by both the base (bimolecular) and the alkyl halide.
    • It is normally undergone by primary substituted alkyl halides but is likely with some secondary alkyl halides and other compounds.
    • The E2 mechanism results in the expansion of a pi bond, the two leaving groups (often a halogen and hydrogen) need to be in antiperiplanar. An antiperiplanar transition state has a staggered arrangement with lower energy than a synperiplanar transition state which is in hidden conformation with higher energy. The reaction mechanism linking staggered conformation is more promising for E2 reactions (unlike E1 reactions).
    • E2 usually uses a strong base. It must be strong enough to eliminate weakly acidic hydrogen.
    • In order for the pi bond to be produced, the hybridization of carbons needs to be dropped from sp3 to sp2.

  • 4. Rearrangement reaction

  • It is a comprehensive class of organic reactions where the carbon frames of a molecule are reorganized to give a structural isomer of the original molecule. Frequently a substituent transfer from one atom to another atom in the same molecule. In the sample below the substituent “R” moves from carbon atom 1 to carbon atom 2:

    Intermolecular reorganizations also take place.

    A rearrangement is not well characterized by simple and distinct electron transfers (represented by curly arrows in organic chemistry textbooks). The real process of alkyl groups passing, as in Wagner-Meerwein reorganization, possibly involves shifting of the alkyl group fluidly along a bond, not ionic bond-breaking and making. It is, still, possible to make the curved arrows for a series of discrete electron transfers that give a similar result as a rearrangement reaction, although these are not essentially realistic. In allylic rearrangement, the reaction is certainly ionic.
    Three important rearrangement reactions are 1,2-rearrangements, olefin metathesis, and pericyclic reactions.

  • 5. Condensation reaction

  • It is a class of an organic addition reaction that continues in a step-wise style to create the addition product, regularly in equilibrium, and a water molecule (later named condensation). The reaction could otherwise include the functional groups of the molecule and development of ammonia, acetic acid ethanol. It is a resourceful class of reactions that can happen in acidic or basic situations or in the existence of a catalyst. This class of reactions is an important part of life as it is crucial to the creation of peptide bonds between amino acids and the biosynthesis of fatty acids.

    There are several kinds of condensation reactions that happen
    Common examples are the aldol Condensation, Knoevenagel condensation, Claisen condensation and the Dieckman condensation (intramolecular Claisen condensation)
    Condensation reaction among two symmetrical aldehydes. The final product is produced irreversibly due to solidity from the conjugation of the double bonds

  • 6. Pericyclic reaction

  • It is a kind of organic reaction wherein the transition state of the molecule has a cyclic configuration, the reaction grows in a concerted style

  • 7. Polymerization reaction

  • In polymer chemistry, polymerization is a method of combining monomer molecules together in a chemical reaction to produce polymer chains or 3-D three-dimensional networks. There are many forms of polymerization and different methods occur to categorize them.

    An example of alkene polymerization is where each styrene monomer’s double bond reforms as a single bond plus a bond to another styrene monomer.