Welcome to my chemistry corner at LearnChemistryByInamJazbi, where reactions unfold like clever stories waiting to be decoded. I’m Inam Jazbi, and I’ve crafted this guide to help students understand organic reactions quickly, clearly, and confidently. Whether you're preparing for MDCAT, ECAT, board exams, or simply strengthening your basics, this post gives you the roadmap you need. Let’s explore how organic molecules transform, rearrange, and dance through reactions!

Organic chemistry may look like a maze, but its reactions follow clear patterns once you meet the main categories. Every reaction — whether it forms bonds, breaks them, swaps atoms, or shifts structures — belongs to a specific family. In this guide, I’ve broken down the Types of Organic Reactions in a way that feels intuitive and exam-ready.

From addition to substitution, from elimination to rearrangement, each reaction type becomes easier once you see how molecules behave. Get ready to unlock the flow of mechanisms with a student-friendly approach crafted on LearnChemistryByInamJazbi.

🧪🌟 Organic Reactions Types | Fast Prep Guide for MDCAT, ECAT + FSC + O & A Levels 

The reactions of organic compounds fall into following classes:

⚛️Substitution reactions

It involves the replacement of an atom or radical (directly attached to a carbon) from a compound (substrate) by another atom or radical.

These reactions are characteristic of saturated organic compounds like alkanes, alkyl halides, benzenes etc.

Substitution reactions are of following six types:

🟦1.I Electrophilic Aromatic Substitution (EAS)/ Electrophilic

Substitution Reactions (ESR/SE)It is a fundamental reaction type exhibited by aromatic compounds. It involves the replacement of one or more H atoms from aromatic ring by an electrophilic specie (E⁺) of unsymmetrical reagent in the presence of Lewis acid catalyst.

It is also known as electrophilic substitution reaction (ESR or SE).

🟦1.II Nucleophilic Substitution Reactions (SN)

It is a fundamental reaction type exhibited by alkyl halides, alcohols etc.

It involves the replacement of weaker nucleophile from electrophilic carbon of a compound by another strong nucleophile.

🟦1.III Nucleophilic Aromatic Substitution

🟦1.IV Free Radical Substitution Reactions

These reactions occur in alkanes. These reactions are initiated by free radicals. The chlorination or bromination of alkanes in the presence of ultraviolet light is an example of free-radical substitution.

⚛️Addition Reaction

1. Addition Reaction involves the combination of two (or more) molecules of substances to form a single molecule of product.

2. In organic chemistry, addition reactions are those in which two or more atoms or groups are simply added across a double or triple (multiple) bond without the elimination of any atom or molecule.

3. In these reactions, at least one p-bond is lost while two new σ-bonds are formed. During addition reactions double bonds become saturated to single bond and triple bonds are converted into double bond or may become saturated by further addition.

4. These reactions are characteristic of unsaturated organic compounds containing C=C or C≡C bonds like alkenes, alkynes, benzenes and carbonyl compounds containing carbonyl group (>C=O) like aldehydes and ketones.

Addition reactions are of following types:

2.I Electrophilic Addition Reactions (EAR)

2.II Nucleophilic addition reactions (NAR) Or Nucleophilic Carbonyl addition (NCA)

2.III Addition Polymerization

🌀2.I. Electrophilic Addition Reactions (EAR)

1. The type of addition reactions in which the species that first attack the multiple bond is an electrophile (electron seeker) are called Electrophilic Addition Reactions (EAR).

2. These reactions proceed by the addition of reacting molecules along the double (or triple) bond.

3. It is called Electrophilic Addition because the reaction is triggered by the attack of an electrophile (an acid or a proton) on the p–electrons of the C-C multiple bonds of alkenes or alkynes (which are weak bases or nucleophiles).

4. Alkenes (or alkynes) are nucleophilic in character due to presence of readily available p–electrons. Thus alkenes (or alkynes) undergo EAR by providing p–electrons to electrophilic reagents.

🔶General Pattern of Mechanism of Electrophilic Addition Reactions (E.A.R.)

Electrophilic Addition Reactions (E.A.R.) proceeds through two steps mechanism. The first step, which is normally the rate-determining step, involves the transfer of the two p–electrons of alkene (or alkynes) to an electrophile of unsymmetrical reagent to generate a carbocation called carbonium ion as a reactive intermediate which react with nucleophile of unsymmetrical reagent to form final addition product.

Step I (Slow Reversible Formation of Carbonium ion by the attack of Electrophilic Hydrogen of Reagent on p–electrons of Alkene)

Step II (Fast Irreversible Attachment of Carbonium ion and Leaving Nucleophilic Group of Reagent Giving Addition Product)

🌀2.II. Nucleophilic Addition Reactions (NAR)/Nucleophilic Carbonyl Addition (NCA)

Nucleophilic Carbonyl Addition (NCA) reactions are the characteristic reactions of carbonyl compounds (i.e. aldehydes and ketones). It is called nucleophilic addition because the reaction is initiated by the attack of nucleophile on the pi-electron of >C=O or double bond of carbonyl compounds.

Such reactions proceed by the addition of reacting molecules along carbon-oxygen double bond(>C=O) of carbonyl compounds.

It is a type of addition reactions in which the species that first attacks the positively polarized carbon of carbonyl group is a nucleophilic negatively polarized atom (i.e. ion) or group having an unshared electron pair.

Nearly all strong nucleophiles (whether ions) like CN-, R-, OR-, OH- or neutral molecules like NH₃, H₂O, NH₂NH₂ (hydrazine) and hydrazine derivatives will attack the low-electron-density center of carbonyl carbon of carbonyl compounds.

Here Nu may be:

1. OH⁻ (in the form of HO – H)

2. CN⁻ (in the form of H-CN)

3. R⁻ (in the form of R-MgX)

4. OR⁻ (in the form of H-OR)

5. NH₂⁻ (in the form of H-NH₂ or H-NHR or H-NR₂)

6. NH₂-NH⁻ (in the form of H-NHNH₂, H-NHNHC₆H₅)

7. ⁻NH< (in the form of H-NR₂)

8. H⁻ (in the form of H – H)

The reagent H - Nu may be of following types:

The carbonyl bond (>C=O) is polarized in all carbonyl compounds due to greater electronegativity of oxygen atom (inductive effect) leaving carbon of carbonyl group electrophilic and oxygen atom nucleophilic. Hence carbon of carbonyl group can be attacked by the donation of a lone pair of electrons from a nucleophilic reagent. The addition of various reagents of the type H-Nu across carbon-oxygen double bond of carbonyl group is characterized by the nucleophilic attack of Nu- of the reagent on the electrophilic carbonyl carbon to form anion followed by the attachment of H+ on the nucleophilic oxygen of carbonyl group to form addition product.

Summary of NCA

Condensation-Elimination (Nucleophilic-Addition-Elimination) Reactions

Carbonyl compounds undergo condensation (Nucleophilic-Addition-Elimination) Reactions with ammonia or its derivatives in which C=O is converted into C=N. It starts with nucleophilic attack on the carbonyl group by the nucleophilic reagents resulting in addition product followed by the elimination of water and condenses into final product.

A number of compounds of the type H–NHZ called derivatives of ammonia add across carbonyl group of carbonyl compounds to form addition product which loses a water molecule to form final product.

The compound H – NHZ may be of following types:

⚛️Elimination reactions

Removal of two atoms or two groups or one atom and one group from a molecule is known as elimination reaction. It involves the removal of one molecule (usually water) of a substance to form more than one products. The product is usually alkene or a compound containing double or triple bond. Elimination reactions are generally endothermic and take place on heating

In elimination reactions the leaving group is removed as a nucleophile and is called a nucleofuge. The following are examples of leaving groups:

Types of Elimination Reactions

Elimination reactions can be classified into two categories:

(a) α-elimination reactions or 1, 1-elimination reactions

(b) β-elimination reactions or 1, 2-elimination reactions

(c) γ-elimination or 1,3-elimination reactions

(d) Extrusion reaction

(c) γ-elimination or 1,3-elimination reactions

A reaction in which both the atoms or groups are removed from the 1st and 3rd positions of the molecule resulting in cyclic compounds is called g-elimination.

(d) Extrusion reaction

A reaction in which a fragment is lost either from a chain or a ring is called extrusion reaction

X –Y–Z → X–Z + Y

(a) α-Elimination Reactions or 1, 1-elimination reactions

A reaction in which both the groups or atoms are removed from the same carbon of the molecule is called a-elimination reaction. This reaction is mainly given by gem dihalides and gem trihalides having at least one α-hydrogen.

Products of the reaction are halocarbenes or dihalocarbenes. Carbenes are key intermediates in a wide variety of chemical and photochemical reactions.

(b) β-Elimination Reactions

Removal of functional group (i.e., leaving group) from α-carbon and other group (generally hydrogen atom) from the β-carbon is called β-elimination reaction.

Consider the following reaction

CH₃–CH₂–CH₂–L → CH₃–CH=CH₂ + H⁺ + L⁻

(1) In this reaction there is loss of two cr bonds and gain of one 7t bond.

(2) Product of the reaction is generally less stable than the reactant.

(3) Reaction is generally endothermic reaction which takes place on heating.

Types of β-Elimination Reactions

In analogy with substitution reactions, β-eliminations can be further subdivided into three categories depending upon the mechanistic pathway. The important aspect is to establish the number of molecules taking part in the elimination step (molecularity of the reaction). The types of β-eliminations are

1) E₂/ Elimination bimolecular

2) E₁/ Elimination unimolecular

3) E₁cB/ Elimination unimolecular conjugate base

⚛️Rearrangement reactions

It involves the rearrangement of different atoms in a molecule with same molecular formula. It is of following types:

(i) Reforming

(ii) Tautomerism

🌟🔥 Summary of Types of Organic Reactions for MDCAT & ECAT 🌟

Organic reactions behave like different “moves” in a chemical dance. Each type transforms molecules in its own style, guided by how bonds break, form, shift or shuffle.

🟦 1. Substitution Reactions (SN / Sᴇ / SF)
One atom/group replaces another.
• Seen in haloalkanes, aromatic compounds
• Can be nucleophilic, electrophilic or free-radical

🟩 2. Addition Reactions
Two molecules merge into one larger molecule.
• Typical for alkenes, alkynes
• Electrophilic, nucleophilic, radical addition

🟨 3. Elimination Reactions
A small group exits, forming double or triple bonds.
• E₁, E₂, dehydration of alcohols
• Opposite of addition

🟪 4. Rearrangement Reactions
Atoms shuffle inside the molecule.
• Carbocation rearrangements
• Hydride shift, methyl shift

🟥 5. Oxidation Reactions
Increase in O or decrease in H.
• Alcohol to aldehyde/ketone
• Alkene to diol or epoxide

🟧 6. Reduction Reactions
Increase in H or decrease in O.
• Carbonyl to alcohol
• Hydrogenation of alkenes

🟫 7. Condensation Reactions
Two molecules join, releasing water or small molecules.
• Esterification, peptide bond formation

🔷 8. Polymerisation Reactions
Small monomers combine to form huge chains.
• Addition polymerisation (ethene → polythene)
• Condensation polymerisation

🎯📦 MCQ Quiz 1 on Types of Organic Reactions (Advanced)

Choose the correct option from coloured boxes.

1️⃣ Dehydration of ethanol to ethene is an example of:
🟥 Substitution
🟦 Addition
🟩 Elimination
🟨 Polymerisation

2️⃣ Reaction of HBr with ethene is:
🟥 Electrophilic substitution
🟦 Electrophilic addition
🟩 Radical elimination
🟨 Nucleophilic substitution

3️⃣ Conversion of alkane to haloalkane using Cl₂ and light is:
🟥 Free-radical substitution
🟦 Electrophilic substitution
🟩 Addition
🟨 Condensation

4️⃣ Oxidation of ethanol to ethanoic acid involves:
🟥 Decrease in oxygen
🟦 Increase in hydrogen
🟩 Increase in oxygen
🟨 No change

5️⃣ Hydrogenation of an alkene gives:
🟥 Alkane
🟦 Alkyne
🟩 Ketone
🟨 Aldehyde

6️⃣ Carbocation rearrangement is characteristic of:
🟥 Nucleophilic addition
🟦 Rearrangement reactions
🟩 Polymerisation
🟨 Oxidation

7️⃣ Esterification is an example of:
🟥 Substitution
🟦 Condensation
🟩 Elimination
🟨 Polymerisation

8️⃣ Breaking a C–X bond and replacing X with OH is:
🟥 Nucleophilic substitution
🟦 Electrophilic addition
🟩 Dehydration
🟨 Polymerisation

9️⃣ Which reaction increases saturation?
🟥 Addition
🟦 Elimination
🟩 Rearrangement
🟨 Oxidation

🔟 Diels–Alder reaction belongs to:
🟥 Polymerisation
🟦 Condensation
🟩 Pericyclic
🟨 Substitution

1️⃣1️⃣ Conversion of benzene to nitrobenzene is:
🟥 Electrophilic substitution
🟦 Nucleophilic substitution
🟩 Radical substitution
🟨 Addition

1️⃣2️⃣ Formation of polythene from ethene is:
🟥 Condensation
🟦 Addition polymerisation
🟩 Elimination
🟨 Reduction

1️⃣3️⃣ Hydride shift takes place in:
🟥 Rearrangement
🟦 Oxidation
🟩 Condensation
🟨 Addition

1️⃣4️⃣ Reaction forming a larger molecule and removing H₂O is:
🟥 Reduction
🟦 Substitution
🟩 Condensation
🟨 Polymerisation

1️⃣5️⃣ Conversion of aldehyde to alcohol is:
🟥 Oxidation
🟦 Reduction
🟩 Substitution
🟨 Elimination
✅ Answers
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🌟🔥 Types of Organic Reactions | Hardcore MDCAT MCQs Quiz🔥🌟
A colour-packed test forged for toppers who love a challenge!

🧪 Choose the correct option from the coloured boxes.

1️⃣ During dehydration of alcohols, carbocation rearrangement occurs due to:
🟥 Higher stability of rearranged carbocation
🟦 Presence of peroxide
🟩 Radical formation
🟨 Steric hindrance

2️⃣ Ozonolysis of alkenes followed by reductive workup gives:
🟥 Alcohols
🟦 Carbonyl compounds
🟩 Carboxylic acids
🟨 Esters

3️⃣ Electrophilic addition to an alkene begins with:
🟥 Nucleophile attack
🟦 Electrophile attack
🟩 Radical formation
🟨 Polymer chain initiation

4️⃣ Which mechanism shows anti-periplanar elimination?
🟥 E₁
🟦 E₂
🟩 SN₁
🟨 SN₂

5️⃣ Nitration of benzene proceeds by formation of:
🟥 NO₂ radical
🟦 NO₂⁺ electrophile
🟩 NO₂⁻ nucleophile
🟨 NO₂H intermediate

6️⃣ Hydrogenation of an alkyne to an alkene requires:
🟥 Lindlar catalyst
🟦 Ni only
🟩 Cu catalyst
🟨 Fe catalyst

7️⃣ The rate of SN₁ reaction mainly depends on:
🟥 Concentration of nucleophile
🟦 Concentration of substrate
🟩 Strength of leaving group only
🟨 Temperature only

8️⃣ Anti-Markovnikov addition of HBr occurs in presence of:
🟥 Light
🟦 Peroxides
🟩 H₂SO₄
🟨 Lindlar catalyst

9️⃣ Example of intramolecular rearrangement is:
🟥 Hydration
🟦 Decarboxylation
🟩 Pinacol–Pinacolone rearrangement
🟨 Nitration

🔟 Oxidation of a primary alcohol under strong conditions gives:
🟥 Aldehyde
🟦 Ketone
🟩 Carboxylic acid
🟨 Alkane

1️⃣1️⃣ Which reaction increases unsaturation?
🟥 Addition
🟦 Substitution
🟩 Elimination
🟨 Reduction

1️⃣2️⃣ Clemmensen reduction converts carbonyl compounds to:
🟥 Alcohols
🟦 Hydrocarbons
🟩 Aldehydes
🟨 Ketones

1️⃣3️⃣ Bromination of benzene requires:
🟥 UV light
🟦 FeBr₃
🟩 NaOH
🟨 Peroxides

1️⃣4️⃣ Formation of tert-butyl carbocation from tert-butyl chloride occurs in:
🟥 SN₂
🟦 SN₁
🟩 E₂
🟨 Electrophilic substitution

1️⃣5️⃣ Hydration of alkene in presence of dilute acid forms:
🟥 Alcohol
🟦 Aldehyde
🟩 Ether
🟨 Ester

1️⃣6️⃣ A concerted reaction with cyclic transition state is:
🟥 Nucleophilic substitution
🟦 Pericyclic
🟩 Condensation
🟨 Oxidation

1️⃣7️⃣ Wurtz reaction produces:
🟥 Alkenes
🟦 Alkanes
🟩 Alcohols
🟨 Aldehydes

1️⃣8️⃣ Dehydrohalogenation is:
🟥 Addition
🟦 Elimination
🟩 Substitution
🟨 Rearrangement

1️⃣9️⃣ Which reaction proceeds with backside attack?
🟥 SN₁
🟦 SN₂
🟩 E₁
🟨 E₂

2️⃣0️⃣ Reduction of ketone with NaBH₄ forms:
🟥 Primary alcohol
🟦 Secondary alcohol
🟩 Tertiary alcohol
🟨 Alkane

✅ ANSWERS (Numbered)
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