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.
Key Formula
R-OH (R = alkyl group)
LaTeX: R\text{-}OH
| Symbol | Meaning | Unit |
|---|---|---|
| R | alkyl group (carbon-containing chain or branch) | none |
| OH | hydroxyl functional group | none |
Worked Example
Problem
Classify each alcohol as primary, secondary, or tertiary: (a) ethanol CH₃CH₂OH, (b) isopropanol (CH₃)₂CHOH, (c) tert-butanol (CH₃)₃COH.
Solution
Step 1: Count the number of carbon atoms directly attached to the carbon that bears the –OH group. (a) Ethanol: –OH is on CH₂, which has one C neighbor (the CH₃) → Primary (1°). (b) Isopropanol: –OH is on CH, which has two C neighbors → Secondary (2°). (c) tert-Butanol: –OH is on C, which has three C neighbors → Tertiary (3°).
Answer
(a) Primary, (b) Secondary, (c) Tertiary
Common Alcohols and Their Properties
| Name | Formula | Class | Boiling Point (°C) | Primary Use |
|---|---|---|---|---|
| Methanol | CH₃OH | Primary | 64.7 | Fuel, solvent, antifreeze |
| Ethanol | C₂H₅OH | Primary | 78.4 | Beverages, antiseptic, fuel |
| Isopropanol | (CH₃)₂CHOH | Secondary | 82.6 | Disinfectant, solvent |
| Glycerol | C₃H₅(OH)₃ | Triol | 290 | Cosmetics, food, pharmaceuticals |
| Benzyl alcohol | C₆H₅CH₂OH | Primary (benzylic) | 205 | Preservative, solvent |
Interactive Tools
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Related Terms
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.
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 Arabic "al-kuhʼl" (the kohl, a fine antimony powder used as eye cosmetic), via Medieval Latin "alcohol." The Arabic term referred to distilled essences; European alchemists applied it to highly purified distillates including "alcohol of wine" (ethanol). The modern chemical meaning was established by Antoine Lavoisier in the late 18th century.