Organic compound
Carbon-based compounds central to life and chemistry.
Organic compounds are a subclass of chemical compounds built around carbon, but chemists lack a single, precise definition; the only universally accepted one is circular, stating that organic compounds are simply the subject matter of organic chemistry. In practice, any large chemical compound containing a carbon–hydrogen or carbon–carbon bond is generally accepted as organic, which includes alkanes like ethane and their derivatives. However, for historical and disciplinary reasons, certain small carbon-containing molecules—such as cyanide ion, hydrogen cyanide, chloroformic acid, carbon dioxide, and carbonate ion—are often excluded. Carbon’s ability to catenate, or form chains with other carbon atoms, enables millions of known organic compounds. Although these compounds make up only a small fraction of Earth’s crust, they are central to life, as all known living organisms are based on them. Living things convert inorganic carbon compounds into organic ones through the carbon cycle, transforming carbon dioxide and a hydrogen source like water into simple sugars and other organic molecules. In industry, synthetic organic compounds are ultimately derived from petrochemicals—hydrocarbons formed by the geologic degradation of biological matter under high pressure and temperature. Historically, organic compounds were defined as those originating in living things, reflecting early-modern vitalism. As vitalism was disproven—notably by Friedrich Wöhler’s syntheses of oxalic acid and urea from inorganic substances—organic chemistry broadened to study all large molecules, which at the time all contained carbon. Organic molecules from biological contexts are now called natural products. In the 20th century, new large molecular species among metal complexes were discovered, but unless they contain carbon, they fall under metalorganic chemistry, not general organic chemistry. In nomenclature, an organyl group, often represented by R, refers to any monovalent substituent with its open valence on a carbon atom.
- field
- Chemistry
- known_for
- Subclass of carbon compounds; basis of all known life
- definition_uncertainty
- Little consensus on exact definition
- key_property
- Carbon catenation enables millions of compounds
Lore & Background
Historically, organic compounds were defined as compounds originating in living things, an expression of early-modern scientific vitalism. Vitalism was a widespread conception that substances found in organic nature are formed by a 'vital force' only living organisms possess. In the 1810s, Jöns Jacob Berzelius argued that a regulative force must exist within living bodies, and contended that compounds could be distinguished by whether they required any organisms in their synthesis. These experiments were followed by many others, disproving vitalism. Although vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds. The modern meaning of organic compound is any compound that contains a significant amount of carbon, even though many known today have no connection to any substance found in living organisms. The term 'carbogenic' has been proposed by E. J. Corey as a modern alternative, but remains obscure. Any definition using simple, broadly-applicable criteria turns out to be unsatisfactory to varying degrees. The modern commonly accepted definition essentially amounts to any carbon-containing compound, excluding several classes traditionally considered inorganic, such as carbides, carbonates, simple oxides of carbon, cyanides, and allotropes of pure carbon.
Reader's Guide
Organic compounds are fundamental to chemistry and biology, yet their definition remains contested. Historically, the concept arose from vitalism, which held that organic substances required a life force. Wöhler's syntheses of oxalic acid and urea from inorganic precursors helped discredit vitalism, but the organic/inorganic distinction persisted. Today, organic compounds are generally understood as carbon-containing compounds, but with many exceptions: carbides, carbonates, simple carbon oxides, cyanides, and pure carbon allotropes are typically excluded. The article notes that even common definitions—such as requiring C–H or C–C bonds—exclude historically important compounds like urea and oxalic acid. This ambiguity extends to organometallic compounds, where it is unclear whether they form a subset of organic compounds. Despite these uncertainties, organic compounds are central to life and industry. Living things incorporate inorganic carbon into organic compounds via the carbon cycle, and synthetic organic compounds are derived from petrochemicals. The field's significance lies in its vast scope—millions of known compounds—and its role in understanding and manipulating the chemistry of life.
Did You Know?
- Little consensus exists among chemists on the exact definition of organic compound; the only universally accepted definition is the quasi-tautological 'organic compounds are the subject matter of organic chemistry.'
- Because of carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known.
- Historically, organic compounds were defined as compounds originating in living things, an expression of early-modern scientific vitalism.
- The term 'carbogenic' has been proposed by E. J. Corey as a modern alternative to 'organic', but this neologism remains relatively obscure.
Frequently Asked Questions
What exactly counts as an organic compound?
At its core, an organic compound is a carbon-based molecule that typically features carbon–hydrogen or carbon–carbon bonds. The field doesn't have one rigid boundary, but most chemists agree that any sizable molecule built around those bonds falls under the umbrella.
Why can't chemists agree on a single definition of organic compounds?
The term has historically been tied to what was studied in organic chemistry rather than a strict structural rule, so the most universally accepted definition is almost circular. In practice, the community leans on the presence of C–H or C–C bonds as a working guideline instead of a hard-and-fast rule.
Why are there millions of known organic compounds?
Carbon's unique ability to bond to itself repeatedly—called catenation—lets it form chains, rings, and complex three-dimensional frameworks. This single property is what gives rise to the staggering diversity of organic molecules we catalog today.
How do organic compounds relate to living organisms?
Every known form of life on Earth is built on organic molecules, from the proteins and nucleic acids inside cells to the lipids in membranes. Despite making up only a tiny fraction of the planet's crust, they are the chemical foundation of biology.
What separates organic compounds from inorganic ones in practice?
The practical dividing line usually comes down to whether the molecule contains carbon bonded to hydrogen or to another carbon atom. Compounds like carbon dioxide or carbonates, which lack those C–H or C–C linkages, are generally treated as inorganic even though they still contain carbon.
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