Early chemists classified compounds as organic if they were derived from living organisms. This was based on the belief that a "vital force" was necessary for their creation and that these compounds couldn't be synthesized in the laboratory.

Some examples of compounds considered organic in the early days include:

* Carbohydrates: Sugars, starches, cellulose

* Proteins: Found in animal tissues and plants

* Fats and oils: Found in plants and animals

* Alcohol: Produced by fermentation of fruits and grains

* Urea: Found in animal urine

This idea of a "vital force" persisted until the mid-19th century when Friedrich Wöhler synthesized urea (a compound found in urine and considered organic) from inorganic materials (ammonium cyanate). This landmark experiment disproved the vital force theory and ushered in the modern understanding of organic chemistry.

Today, organic chemistry is defined as the study of carbon-containing compounds, regardless of their origin.