Functional Group
A functional group is a specific atom or group of atoms within an organic molecule that determines its characteristic chemical reactions and physical properties. Functional groups are the reactive centers of organic molecules; the carbon skeleton (backbone) largely determines size and shape, while the functional group dictates behavior. Identifying functional groups is the foundation of systematically predicting and classifying organic reactions.
Major Organic Functional Groups
| Functional Group | Formula | Class of Compound | Example | Characteristic Reaction |
|---|---|---|---|---|
| Hydroxyl | –OH | Alcohol | Ethanol | Esterification, oxidation |
| Carboxyl | –COOH | Carboxylic acid | Acetic acid | Neutralization, esterification |
| Amino | –NH₂ | Amine | Methylamine | Basicity, amide formation |
| Carbonyl (ketone) | C=O (internal) | Ketone | Acetone | Nucleophilic addition |
| Carbonyl (aldehyde) | –CHO | Aldehyde | Formaldehyde | Oxidation to acid |
| Ester | –COO– | Ester | Ethyl acetate | Saponification |
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Related Terms
Alcohol (organic)
In organic chemistry, an alcohol is a compound in which a hydroxyl group (–OH) is bonded to a saturated carbon atom. Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) based on how many carbon atoms are attached to the carbon bearing the –OH group. They are among the most versatile compounds in synthesis and commerce, serving as solvents, antiseptics, fuels, and precursors to aldehydes, ketones, and carboxylic acids.
Carboxylic Acid
A carboxylic acid is an organic compound containing a carboxyl group (–COOH), which consists of both a carbonyl (C=O) and a hydroxyl (–OH) group attached to the same carbon. Carboxylic acids are weak acids that partially dissociate in water to donate a proton (H⁺) from the –OH group, with the resulting carboxylate anion stabilized by resonance. They are widespread in biology (amino acids, fatty acids, citric acid cycle intermediates) and industry (acetic acid for vinegar, benzoic acid as a preservative).
Ester (organic)
An ester is an organic compound formed when a carboxylic acid reacts with an alcohol in a condensation reaction (esterification), with the loss of a water molecule, producing the functional group –COO– (or –RCOOR'). Esters are responsible for many characteristic fruit aromas and flavors, and they occur naturally in fats and oils (triglycerides are esters of glycerol and fatty acids). Industrially, esters are used as plasticizers, solvents, perfumes, and biodiesel components.
From Latin "functio" (performance, execution). The concept was developed progressively in the 19th century as chemists realized that certain atomic groupings, regardless of the carbon skeleton, consistently produced the same types of reactions. The term was formalized in organic chemistry curricula by the early 20th century.