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4.2: Background

Difficulty Level: At Grade Created by: CK-12

An alcohol is defined as a hydrocarbon with a hydroxyl (-OH) functional group. This group includes methanol, ethanol, propanal, butanol, and more.

ROH\begin{align*}\mathrm{R}-\mathrm{OH}\end{align*}

Diagram of an alcohol molecule. The “R” represents the rest of the compound.

Alcohols are useful for many purposes because of their behavior in water. Alcohols are polar and capable of forming hydrogen bonds with water. The bond between the carbon and the oxygen is exceptionally strong, so the hydroxyl group cannot be removed by water and remains a part of the hydrocarbon. The more negatively charged oxygen will pull the hydrogen atoms in the water molecules towards it, causing the alcohol molecules to separate. For these reasons, most alcohols are soluble, or capable of dissolving, in water. This property is important to industry today, as about 55% of ethanol produced synthetically is used to create solvents.

Alcohol is soluble in both water and lipids, or fats. While the “-OH” end of the alcohol molecule is hydrophilic, or attracted to water, the hydrocarbon chain attached to it is hydrophobic, or repelled by water. The hydrocarbon chain is miscible in lipids and gives alcohol its fat-soluble properties.

Alcohols can act as either a base or an acid because they are capable of attracting and donating hydrogen ions (H+). They are generally slightly more basic than water and share many properties with other bases. For example, alcohols usually taste bitter and feel slippery.

When naming alcohols, start by counting the number of carbons in the compound and give it the correct prefix. Alcohols are distinguished from alkanes by adding “–anol,” instead of “-ane,” to the prefix. For all other compounds than methanol, specify which carbon the hydroxyl group is bounded to by following the IUPAC scheme.

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