How Organic Chemistry Is Currently Defined as the Study of Carbon Compounds

Organic chemistry is the branch of chemistry concerned with carbon compounds. The International Union of Pure and Applied Chemistry (IUPAC) defines it as “the chemistry of compounds of carbon” (IUPAC Gold Book). In practice, the field studies their structures, properties, reactions, and preparation. The Encyclopaedia Britannica gives a similar description, focusing on the structure, properties, and reactions of carbon-containing compounds (Encyclopaedia Britannica).

The definition covers compounds with a wide range of structures, from small molecules to large polymers. Many contain carbon bonded to hydrogen, oxygen, nitrogen, sulfur, or halogens. Carbon can also bond to itself, forming chains and rings. These patterns create the variety of structures that organic chemists study.

What counts as an organic compound?

Hydrocarbons contain only carbon and hydrogen. Methane and benzene are examples. Other organic compounds have functional groups attached to a carbon framework. An alcohol contains a hydroxyl group, while a carboxylic acid contains a carboxyl group. Polymers also fall within the field when they are built from carbon-containing units.

Carbon alone is not enough to classify every compound as organic. Chemists traditionally treat several simple carbon-containing substances as inorganic, including carbon monoxide, carbon dioxide, carbonates, and cyanides. The boundary is a convention used in chemistry, so a compound’s classification depends on its type and structure, not only on whether its formula contains carbon.

One example: acetic acid

Acetic acid, CH₃COOH, is an organic compound. It contains carbon and is not one of the commonly excluded simple carbon-containing substances. Its carboxyl group consists of a carbon atom double-bonded to oxygen and single-bonded to a hydroxyl group.

This example shows how the definition works in practice: carbon content is the starting point, while the compound’s structure helps identify what kind of carbon compound it is.

Why does the definition refer to carbon?

Carbon forms bonds with itself and with many other elements. Its ability to form chains and rings gives rise to a broad range of molecular structures. Functional groups attached to those structures affect how compounds react and what properties they have.

For example, an alcohol and an ether can contain the same elements but have different structures and chemical behavior. Organic chemistry organizes compounds by these structures and by the reactions they undergo.

The field overlaps with biology because many molecules in living systems contain carbon. Biochemistry studies the chemistry of those molecules. Organic chemistry also covers carbon compounds made in laboratories and industrial settings; a compound does not need to come from a living organism to be organic.

How did the definition change?

Organic chemistry was once associated with substances obtained from living things. In the nineteenth century, the idea that such compounds required a special “vital force” lost support as chemists prepared organic compounds from non-living materials.

In 1828, Friedrich Wöhler prepared urea from ammonium cyanate in a laboratory. Urea was known as a substance produced by living organisms, so the synthesis challenged the idea that organic compounds could form only through life. The definition came to focus on the chemistry of carbon compounds, not on where a compound originated.

That history also explains why the modern definition is not a perfect rule for every carbon-containing substance. Chemists use conventional classifications for compounds such as carbonates and carbon oxides.

Key Takeaways

• IUPAC defines organic chemistry as the chemistry of compounds of carbon (IUPAC Gold Book).
• The field studies the structures, properties, reactions, and preparation of carbon compounds.
• Carbonates, carbon oxides, and cyanides are among the carbon-containing substances traditionally classified as inorganic.
• Organic compounds can come from living organisms or be made in laboratories and industrial settings.
• Acetic acid, CH₃COOH, is an example of an organic compound.