As we know that organic chemistry is all about the study of carbon containing compounds, their features and interactions. It involves a diverse range of concepts, from the nature of chemical bonding to the structural diversity of organic molecules. Understanding these fundamental and basic concepts is essential for exploring more complex topics such as reaction mechanisms and functional group behavior. This article explains the fundamental concepts, including covalent bonding, isomerism key types of organic reactions and many more. It will definitely provide a solid groundwork for further study.l.toLowerCase().replace(/\s+/g,"-")" id="c2ba244a-5521-4112-924f-5bbe2ca5d02c" data-toc-id="c2ba244a-5521-4112-924f-5bbe2ca5d02c">Covalent bondA covalent bond is formed when two atoms share a pair of electrons to get a stable and lower-energy state just like noble gases. Unlike ionic bonds, where atoms transfer electrons, covalent bonds involve sharing electrons. Each atom contributes at least one valence electron to form the bond. The nuclei of both atoms attract the shared electrons and hold them together. Covalent bonds form only if the bonded atoms have lower total energy than when they are separate. The overlap of atomic orbitals and the number of shared electrons determine the strength of a covalent bond. Covalent bonds exist in many common substances, both organic and inorganic.Inorganic compounds with covalent bonds:Organic compounds with covalent bonds:Diatomic molecules including Hydrogen (H₂), Nitrogen (N₂), Oxygen (O₂) and Chlorine (Cl₂) are covalent compounds. Water (H₂O) is also a covalent in nature where oxygen shares electrons with two hydrogen atoms. Carbon forming two double bonds with oxygen is another example of covalent molecule.All carbon-based molecules, such as carbohydrates, proteins, lipids, and nucleic acids (DNA/RNA) have covalent bonds. Hydrocarbons like methane (CH₄), ethane (C₂H₆), and benzene (C₆H₆) are also covalent in nature.How to Represent Covalent BondsIn structural formulas, covalent bonds are shown as lines connecting atoms as shown below;· Single bond (—) → one shared electron pair. Examples include H—H, Cl—Cl).· Double bond (=) → Two shared electron pairs such as in O₂ (O=O).· Triple bond (≡) → Three shared electron pairs. Examples are C≡O and N≡N.Each bond type influences the strength and reactivity of a molecule. Single bond is the weakest but longest with one sigma (σ) bond. Double bonds are stronger than single bonds because they contain one σ and one pi (π) bond. Triple bonds are the strongest and shortest. Each triple bond contain one σ and two π bonds. Molecules with multiple bonds are more reactive as π bonds are weaker than σ bonds. They break more easily during chemical reactions.Properties of Covalent Bonds:Atoms form covalent bonds by sharing electrons. If one pair of electrons is not enough to satisfy an atom’s valency, more than one pair can be shared. Some characteristics of covalent bonds are:No new electrons are formedThe bond only formed with existing electrons.Directional natureAtoms are arranged in a specific directions.Low melting and boiling pointsCovalent compounds melt or boil at relatively low temperatures.Low enthalpy of vaporization and fusionThey require less energy to change states.Poor conductors of electricityThey cannot conduct electricity due to the absence of free electrons.Insoluble in waterMost covalent compounds do not dissolve in water.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="e62c0500-96d4-4ac9-bc98-90c14c8fc7fb" data-toc-id="e62c0500-96d4-4ac9-bc98-90c14c8fc7fb">1. Polar Covalent Bond:In a polar covalent bond the electrons are shared unequally between two atoms due to a difference in their electronegativity values. The atom having higher electronegativity attracts the shared electrons towards itself. It develops a partial negative charge (δ⁻), while the other atom develops a partial positive charge (δ⁺). The difference in electronegativity between the bonded atoms is greater than zero and less than 2.0 in polar bonds. The unequal electron distribution forms the dipoles within the molecule.In a water molecule (H₂O), oxygen is more electronegative than hydrogen. It pulls the shared electrons more strongly to itself. This pull develops a partial negative charge on the oxygen atom and partial negative charge on the hydrogen atoms. Thus polarity is induced which enables water molecule to form hydrogen bonds.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="4c4c6e5d-ec3f-46fe-9115-243308d4b348" data-toc-id="4c4c6e5d-ec3f-46fe-9115-243308d4b348">2. Nonpolar Covalent Bond:A nonpolar covalent bond is formed when electrons are shared equally between two atoms. It happens because atoms have same or nearly identical electronegativity values. Charges are not separated within the molecule. It means that the electron distribution is completely balanced.In an oxygen molecule (O₂), hydrogen gas (H₂) and nitrogen gas (N₂) electrons are shared equally and they show nonpolar covalent bonding.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="3a05b46a-878b-48c0-8d40-34372cdde62d" data-toc-id="3a05b46a-878b-48c0-8d40-34372cdde62d">2. The Lewis ModelAn American chemist G.N. Lewis in 1916 introduced the concept that two electrons can be shared between two atoms and serve as the link between them. He described the formation of such bonds as resulting from the tendencies of certain atoms to combine with one another. Both atoms achieve the electronic structure of a corresponding noble gas atom. In Lewis structures, the shared pair of electrons is known as bonding electron pair and represented by a single line (—) between two atoms. In addition to bonding pairs, atoms may also have lone pairs of electrons. Lone pairs are non-bonding electrons. They remain on the atom and do not contribute to the bond formation. Below are some steps to make a Lewis structure:· Counting the total number of valence electrons available for bonding.· Placing the chemical symbols of the elements in an arrangement that reflects their connectivity.· Adding a single bonding pair between each linked pair of atoms.· Distributing the remaining electrons so that each atom achieves a complete valence shell· Finally representing each bonding pair with a line (—) and lone pairs as dots (..).l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="7f0391ff-d9e6-4997-ae08-45b142e20aa8" data-toc-id="7f0391ff-d9e6-4997-ae08-45b142e20aa8">3. ResonanceResonance is the polarity induced in a molecule by the interaction of a lone pair of electrons with a pi bond. It is also the interaction of two pi bonds in nearby atoms. Multiple Lewis structures are possible for a molecule containing multiple bonds. Such as ozone (O₃) in which central oxygen atom must be equally bonded to both terminal oxygen atoms. According to Lewis concept, when more than one valid Lewis structure can be drawn for a molecule, a single structure alone does not fully represent the actual structure of it. Instead, the true structure is a hybrid of all possible Lewis structures. It also suggests that certain electrons are delocalized. Delocalization means that they are not confined to a single bond but are instead shared across multiple atoms. A double-headed arrow (↔) is used to indicate resonance.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="b45f07fd-68a5-42fd-8c73-c8498d2a00f1" data-toc-id="b45f07fd-68a5-42fd-8c73-c8498d2a00f1">4. Conjugated systemsA conjugated system refers to a molecular structure in which single and double bonds alternate along the carbon backbone. This alternating bond pattern allows electron delocalization. It enables the formation of charged lattice distortions. As a result, conjugated systems exhibit electrically conductive behavior. This phenomenon make them important in various chemical and electronic applications. They have useful role in organic semiconductors and conductive polymers.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="5b2a1661-9a27-45ba-8f1a-5b91b6ac43d8" data-toc-id="5b2a1661-9a27-45ba-8f1a-5b91b6ac43d8">5. Classification of Organic CompoundsMostly compounds around us are organic in nature. Due to this reason, it is essential to classify them into distinct categories. It is essential for their systematic study. They are classified on the basis of the arrangement of carbon atoms in their structure. They can be;1. Acyclic or Open Chain Compounds2. Cyclic or Closed Chain Compoundsl.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="21492ea0-4a5b-42dd-8bd3-560cd123586d" data-toc-id="21492ea0-4a5b-42dd-8bd3-560cd123586d">1. Acyclic or Open Chain CompoundsIn acyclic compounds, carbon atoms form an open-chain structure which can be either straight or branched. These compounds are also called aliphatic compounds.· Straight Chain Compounds: They have a continuous carbon chain without any branches. Some common examples are mentioned below,· Branched Chain Compounds: The carbon chain contains branches in these kinds of compounds. Such as;l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="55166ac0-3f96-4682-bf04-49c08c0e0ecd" data-toc-id="55166ac0-3f96-4682-bf04-49c08c0e0ecd">2. Cyclic or Closed Chain CompoundsCyclic compounds contain one or more rings in their structure. They can be;a. Homocyclic or Carbocyclic Compoundsb. Heterocyclic Compoundsl.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="abb795a8-3b65-4b3f-a277-b03f67810e90" data-toc-id="abb795a8-3b65-4b3f-a277-b03f67810e90">a. Homocyclic or Carbocyclic CompoundsThese compounds consist entirely of carbon atoms and are further divided into:Alicyclic Compounds:These compounds are similar to aliphatic compounds in their properties. Examples are;Aromatic Compounds:They are cyclic unsaturated compounds known for their fragrant smell. They originated from the Greek word Aroma meaning fragrance. These compounds are further classified into:1. Benzenoid Aromatic CompoundsThese compounds consist of one or more benzene rings which are either isolated or fused. They might be Monocyclic (one benzene ring), Bicyclic (two benzene rings) or Tricyclic (three benzene rings).2. Non-Benzenoid Aromatic CompoundsThese compounds have highly unsaturated rings in place of benzene. Such as;l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="20fe9324-59e9-4bba-ac40-b4521fe225c3" data-toc-id="20fe9324-59e9-4bba-ac40-b4521fe225c3">b. Heterocyclic CompoundsThe compounds having cyclic structures one or more heteroatoms such as oxygen, nitrogen within the ring are termed as heterocyclic. They can be:l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="0fa363bf-a200-4850-a140-b73585ee2049" data-toc-id="0fa363bf-a200-4850-a140-b73585ee2049">· Alicyclic Heterocyclic Compounds:The compounds comprising of one or more heteroatoms inside the ring and resemble aliphatic compounds are alicyclic.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="e7039b5d-59e5-4c61-b05b-25842fba6169" data-toc-id="e7039b5d-59e5-4c61-b05b-25842fba6169">· Aromatic Heterocyclic Compounds:Aromatic heterocyclic compounds have one or more heteroatoms in the ring skeleton and exhibits aromatic properties.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="5e3ef873-cb28-4c8e-9046-97718c8b47e3" data-toc-id="5e3ef873-cb28-4c8e-9046-97718c8b47e3">6. IsomerismIsomers are the compounds with same molecular formula but different structural or spatial arrangements of atoms. Isomers have different and distinct physical and chemical properties. The term “isomer” is derived from the Greek words “isos” and “meros” meaning equal parts. Swedish chemist Jacob Berzelius introduced this concept in 1830.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="91339e94-15f0-442b-9942-40b469a284c5" data-toc-id="91339e94-15f0-442b-9942-40b469a284c5">Types of Isomerism Isomerism is classified into Structural Isomerism and Stereoisomerism with further subtypes.l.toLowerCase().replace(/\s+/g,"-")" id="927c547c-2dab-44ef-9672-c36338bc18d3" data-toc-id="927c547c-2dab-44ef-9672-c36338bc18d3">1. Structural Isomerism/Constitutional Isomerism:Molecules having the same molecular formula but different functional groups or arrangement of atoms show Structural isomerism. It can be;a. Chain IsomerismChain isomerism also known as Skeletal Isomerism. It occurs when compounds have the same molecular formula but different arrangements of carbon atoms. It results in straight or branched chains. Pentane exists in following isomers;· n-Pentane (straight-chain)· Isopentane (branched-chain)· Neopentane (highly branched)l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="ad664df9-776d-41bb-a685-00a1037ec221" data-toc-id="ad664df9-776d-41bb-a685-00a1037ec221">b. Position IsomerismThe type of isomerism in which molecular formula is same but the functional group is attached at different positions within the carbon chain. exists as;l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify">c. Functional IsomerismFunctional isomers have the same molecular formula but different functional groups. have two isomers Propanal with aldehyde group (CHO) and Acetone with ketone group (CO).l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify">d. MetamerismThe compounds have different alkyl groups and are attached to a divalent functional group such as oxygen, sulfur, or nitrogen. O exhibits following isomers;e. TautomerismIn Tautomerism isomers rapidly interconvert by shifting a proton and electrons within the same molecule. Both are usually in equilibrium. Such as Keto-Enol Tautomerism.Keto form ⇌ Enol formf. Ring-Chain IsomerismRing-chain isomerism arises when one isomer has an open-chain structure, while another has a cyclic or ring structure. exists as Propene (open-chain) and Cyclopropane (cyclic).l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify">l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="887c4c81-bd00-4785-9409-5c392c805ce0" data-toc-id="887c4c81-bd00-4785-9409-5c392c805ce0">2. StereoisomerismStereoisomers are the compounds exhibiting the same molecular formula and connectivity but different three-dimensional spatial arrangement of atoms.l.toLowerCase().replace(/\s+/g,"-")" id="cd6223c0-4705-4788-b0ea-0cc30ae56160" data-toc-id="cd6223c0-4705-4788-b0ea-0cc30ae56160">a. Geometrical IsomerismGeometrical isomerism also known as Cis-Trans Isomerism occurs due to restricted rotation around a double bond or within a ring system. It leads to different spatial arrangements of atoms. For example in Cis and Trans compounds.b. Optical IsomerismOptical isomers have the same structure but exist as non-superimposable mirror images, known as enantiomers. These isomers rotate plane-polarized light differently. Such as Dextro (D) and Laevo (L) forms of glucose.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="8e5d787f-a7b2-4d1a-8e85-b5430e9d73d5" data-toc-id="8e5d787f-a7b2-4d1a-8e85-b5430e9d73d5">7. Types of Organic ReactionsReactions happen all around us. You must be amazed after knowing that there are types of organic reactions. The knowledge and study of the types of organic reactions is necessary to understand organic compounds.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="22bcc365-275a-4087-9b16-9b60a14432fd" data-toc-id="22bcc365-275a-4087-9b16-9b60a14432fd">Types of Organic ReactionsThere are five main types of organic reactions which are given as follows:· Substitution reactions· Elimination reactions· Addition reactions· Radical reactions· Oxidation-Reduction Reactionsl.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="2d59e10c-2aaa-4a3b-8b94-6bc08716fd87" data-toc-id="2d59e10c-2aaa-4a3b-8b94-6bc08716fd87">1. Substitution Reactions In a substitution reaction one atom or a group of atoms replaces another atom or a group of atoms in a molecule resulting in the formation of a new substance. In a nucleophilic substitution reaction, the presence of pair of electrons is compulsory and it should have a high affinity for the electropositive species than the already present group. These reactions take place at low temperature. A strong base such as NaOH has to be in dilute form because if it is of higher concentration, there are chances of dehydro halogenation in the reaction. The solution should be in an aqueous state for the reaction to take place. The types of Substitution reactions include nucleophilic substitution reactions such as Nucleophilic Acyl substitution and electrophilic substitution reactions.l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="4009f97b-b280-4d5c-b908-6ebd4b058a7e" data-toc-id="4009f97b-b280-4d5c-b908-6ebd4b058a7e">2. Elimination ReactionsElimination reactions involve the elimination and removal of the adjacent atoms. During this multiple bonds are simultaneously formed and there is a release of small molecules as by products. One of the examples of elimination reaction is the conversion of ethyl chloride to ethylene.CH3CH2Cl → CH2= CH2 + HCl l.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="54b8604c-62ae-45ba-b62c-3bd34e1147b2" data-toc-id="54b8604c-62ae-45ba-b62c-3bd34e1147b2">3. Addition ReactionsAn addition reaction is opposite of an elimination reaction. In such reaction molecules are added to the carbon-carbon multiple bonds. In the reaction given below when HCl is added to ethylene, it will give ethylene chloride.HCl + CH2 = CH2 → CH3CH2Cll.toLowerCase().replace(/\s+/g,"-")" style="text-align: justify" id="5a9360f1-e5ef-4b7b-bacf-097396b789de" data-toc-id="5a9360f1-e5ef-4b7b-bacf-097396b789de">4. Radical ReactionsMany organic reactions involve radicals and their movement such as addition of a halogen to a typically saturated hydrocarbon involves free radical mechanism. Three steps are involved in a radical reaction. They include initiation, propagation, and termination simultaneously. Initially the weak bond is broken and free radical initiates the reaction. After the formation of free radicals halogen it is added to the hydrocarbon and it gives alkyl halide.Referenceshttps://www.britannica.com/science/covalent-bondhttps://www.khanacademy.org/science/organic-chemistryhttps://www.toppr.com/bytes/organic-chemistry-basics/http://en.wikipedia.org/wiki/Chemical_bondhttps://www.sciencedirect.com/topics/physics-and-astronomy/conjugated-systemhttps://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/nomen1.htmhttps://www.toppr.com/guides/chemistry/organic-chemistry/classification-organic-compounds/https://www.toppr.com/guides/chemistry/organic-chemistry/types-of-organic-reactions/