Organic chemistry is the study of carbon-containing compounds and their properties, structures, compositions, reactions, and synthesis. Carbon’s unique ability to form stable covalent bonds with other carbon atoms (catenation) and with a wide variety of other elements — hydrogen, oxygen, nitrogen, sulfur, phosphorus, and the halogens — gives rise to millions of known organic compounds. The central role of carbon in living systems and in synthetic materials makes organic chemistry essential to biochemistry, pharmaceuticals, polymers, agrochemicals, and materials science.
Carbon’s electronic configuration (1s²2s²2p²) allows it to adopt three hybridization states that determine molecular geometry. In sp³ hybridization, four equivalent orbitals point to the corners of a tetrahedron (109.5° bond angle), as in methane (CH₄) and alkanes. sp² hybridization produces three coplanar orbitals at 120° with one unhybridized p orbital available for pi bonding, characteristic of alkenes. sp hybridization gives two linear orbitals at 180° and two unhybridized p orbitals, found in alkynes. This versatility in bonding geometry underpins the structural diversity of organic molecules.
Functional groups are specific groups of atoms within molecules that confer characteristic chemical reactivity. The major families include alkanes (C–C single bonds), alkenes (C=C), alkynes (C≡C), alcohols (–OH), ethers (C–O–C), aldehydes (–CHO), ketones (C=O), carboxylic acids (–COOH), esters (–COOR), amines (–NH₂), and aromatic rings. Each functional group undergoes predictable reactions, allowing chemists to design synthetic pathways and predict product structures. The concept of functional groups is the organizing principle of organic chemistry.
IUPAC nomenclature provides a systematic method for naming organic compounds. The process involves: (1) identifying the parent chain — the longest continuous carbon chain containing the principal functional group; (2) numbering the chain to give the functional group and substituents the lowest possible locants; (3) naming substituents (alkyl groups, halogens, etc.) in alphabetical order with their position numbers; (4) assigning functional group priority — carboxylic acids > esters > aldehydes > ketones > alcohols > amines > alkenes > alkynes > alkanes. The name is assembled as prefix + parent + suffix, with hyphens separating numbers and commas separating numbers from each other.
Isomerism — the existence of compounds with the same molecular formula but different structures — is a central theme in organic chemistry. Structural isomerism includes chain isomerism (different carbon skeletons), position isomerism (different location of functional groups), and functional group isomerism (different functional groups). Stereoisomerism involves the same connectivity but different spatial arrangement, divided into geometric isomerism (cis/trans or E/Z) and optical isomerism (chirality, enantiomers, diastereomers). Understanding isomerism is critical for predicting physical properties and biological activity.
The historical development of organic chemistry began with the vital force theory (Berzelius, 1807), which held that organic compounds could only be produced by living organisms. Friedrich Wöhler’s synthesis of urea from ammonium cyanate in 1828 disproved this theory and launched synthetic organic chemistry. The 19th and 20th centuries saw the elucidation of structure theory (Kekulé, Couper), the tetrahedral carbon atom (van ‘t Hoff, Le Bel), and the development of mechanistic organic chemistry (Ingold, Robinson). Today, organic chemistry continues to expand through retrosynthetic analysis, organometallic chemistry, and the synthesis of increasingly complex natural products and designed molecules.
