Organic Chemistry is the branch of chemistry concerned primarily with carbon containing compounds, their structures, properties, reactions, mechanisms, synthesis, analysis, and applications. Carbon is unusually versatile because it forms strong covalent bonds with itself and with elements such as hydrogen, oxygen, nitrogen, sulfur, phosphorus, and the halogens. Carbon can form chains, branches, rings, aromatic systems, multiple bonds, three dimensional frameworks, and extensive polymer structures.
The historical name organic arose from the old idea that substances from living organisms required a special vital force, but modern organic chemistry rejects that distinction. Synthetic compounds and naturally occurring compounds are studied using the same chemical principles. Some simple carbon containing substances, including many carbonates and certain carbides, are generally treated as inorganic rather than organic.
Functional groups provide one of the main systems for organising organic chemistry. Alcohols contain hydroxyl groups attached to carbon frameworks, ethers contain oxygen between carbon groups, aldehydes and ketones contain carbonyl groups, carboxylic acids contain carbonyl and hydroxyl functionality, esters contain characteristic carbonyl oxygen arrangements, amines contain nitrogen based functional groups, amides contain nitrogen attached to carbonyl carbon, and alkyl halides contain carbon halogen bonds. Alkenes contain carbon carbon double bonds and alkynes contain carbon carbon triple bonds. Aromatic compounds possess special delocalised electronic structures and characteristic stability and reactivity. Functional group classification allows chemists to predict broad patterns while recognising that molecular environment, steric effects, electronic effects, solvent, temperature, catalysts, and neighbouring groups can substantially modify behaviour.
Organic structures can be represented using molecular formulas, structural formulas, condensed formulas, skeletal formulas, and three dimensional models. Molecular formulas indicate elemental composition but cannot uniquely specify connectivity. Structural formulas reveal atom connections, while skeletal representations simplify carbon frameworks by omitting many carbon and hydrogen labels. Isomers have the same molecular formula but different molecular arrangements. Constitutional isomers differ in connectivity, while stereoisomers have the same connectivity but different spatial arrangements. Enantiomers are non superimposable mirror images, while diastereomers are stereoisomers that are not mirror images. Stereochemistry is important because two compounds with identical connectivity and different spatial arrangements can have very different biological, physical, and chemical properties.
Organic reactions include substitution, addition, elimination, rearrangement, oxidation, reduction, condensation, hydrolysis, coupling, and numerous specialised transformations. Substitution replaces one atom or group with another, addition adds groups across a multiple bond, and elimination removes groups to generate a new multiple bond or related unsaturated structure. Reaction mechanisms describe how bonds break and form and may involve ionic intermediates, radicals, concerted processes, or catalytic cycles. Mechanistic reasoning considers electron rich and electron poor sites, bond polarity, steric effects, resonance, inductive effects, solvent, temperature, and leaving group ability. Understanding mechanisms allows chemists to predict products and side reactions rather than relying entirely on memorised reaction lists.
Organic synthesis is the planned construction of complex molecules from simpler starting materials. Retrosynthetic analysis works backwards from a target structure to identify strategically useful disconnections and simpler precursors. Chemists consider bond forming methods, functional group compatibility, chemoselectivity, regioselectivity, stereoselectivity, reaction yield, purification, reagent availability, safety, scalability, and waste generation. Protecting groups can temporarily deactivate reactive functionality, although they add steps and waste and are therefore avoided when possible. Catalysts can increase reaction rates and improve selectivity. Modern synthetic chemistry increasingly seeks shorter routes, fewer purification steps, lower waste, safer reagents, renewable feedstocks, and higher atom economy.
Organic chemistry is deeply connected with biology because proteins, carbohydrates, lipids, nucleic acids, metabolites, pigments, hormones, vitamins, and many signalling molecules contain carbon based structures. Biochemical reactions follow organic principles involving functional groups, stereochemistry, acid base equilibria, redox chemistry, nucleophilic and electrophilic reactions, and catalytic mechanisms. Medicinal chemistry applies organic chemistry to the design and optimisation of molecules that interact with biological targets. Small changes in molecular structure can alter potency, selectivity, absorption, distribution, metabolism, excretion, and toxicity. Hydrogen bonding, ionic interactions, hydrophobic effects, covalent bonding, molecular shape, and conformational flexibility can all influence how an organic molecule interacts with a biological macromolecule.
Industrial organic chemistry supports the manufacture of fuels, polymers, pharmaceuticals, solvents, dyes, detergents, coatings, adhesives, fragrances, agricultural chemicals, electronic materials, and many other products. Petroleum and natural gas have historically supplied major carbon feedstocks, while biomass, recycled carbon, carbon dioxide derived routes, and other alternatives are increasingly studied. Polymer chemistry uses organic monomers to produce materials with tailored mechanical, thermal, optical, electrical, and chemical properties. Industrial processes must optimise yield, selectivity, catalyst performance, energy consumption, raw material cost, safety, waste generation, emissions, purification, and product consistency. Laboratory reactions that work on a small scale may require substantial redesign before becoming economically and safely practical at industrial scale.
Organic chemistry developed from early studies of natural substances into a systematic science of molecular structure and reactivity. Major developments included the recognition that compounds associated with living organisms could be synthesised from nonliving materials, the establishment of structural theory, advances in stereochemistry, spectroscopy, chromatography, mechanistic chemistry, and modern computational methods. Nuclear magnetic resonance spectroscopy, infrared spectroscopy, mass spectrometry, ultraviolet visible spectroscopy, chromatography, and crystallographic techniques provide complementary information about molecular identity and structure. Contemporary organic chemistry includes organometallic chemistry, photochemistry, catalysis, supramolecular chemistry, polymer chemistry, medicinal chemistry, materials chemistry, green chemistry, and automated synthesis. The field remains central to understanding how molecular structure controls chemical behaviour and to designing substances with deliberately chosen properties.
