Alcohol in Chemistry: Types, Uses & Formula

Instructor: Sarah Pierce

Sarah has a doctorate in chemistry, and 12 years of experience teaching high school chemistry & biology, as well as college level chemistry.

This lesson describes how to recognize and name alcohols. Monohydric, dihydric, and polyhydric alcohol classifications are discussed as well as primary, tertiary, and secondary alcohol groups. The properties of alcohols and reactivity is also covered.

What is an Alcohol?

Sitting in a bar drinking a beer, have you ever wondered, ''What is in this drink that makes me feel so relaxed?'' You probably already know the answer is alcohol, specifically ethanol, but have you ever wondered what exactly alcohol is? Alcohol molecules are organic molecules that contain an -OH group. This -OH group makes the molecule reactive, so it is called a functional group.

Alcohol functional groups are found in biological molecules such as sugars, amino acids, and vitamins. Alcohol functional groups are also found in molecules that are used every day. You can find ethanol in drinks like wine, beer, vodka, whiskey, gin, and rum, among many others. Ever had to check the antifreeze levels in your car? It contains ethylene glycol, another alcohol.

Structure of ethylene glycol
Ethylene Glycol

Nomenclature

The alcohol functional group hydroxyl is an -OH group. When naming alcohols, the -e is removed from the hydrocarbon name and an -ol suffix is added. A number in front of the hydrocarbon name tells the location of the alcohol group.

For example, in 1-butanol, there are four carbon atoms, so the parent hydrocarbon name is butane. The -e is dropped from butane and -ol is added, resulting in butanol. The 1 indicates the alcohol group is on the first carbon.

1-butanol
1-butanol

The carbon chain should be numbered so that the alcohol has the lowest number. When naming the molecule 1-butanol, you can either name it as 4-butanol or 1-butanol, depending on which side of the molecule you begin to count. Since 1 is a smaller number than 4, 1-butanol is correct. If there are two alcohol groups on a molecule the suffix is changed to -diol.

Alcohol Molecule Classification

Molecules can be classified based on the number of alcohol groups.

  • monohydric -one alcohol group on the molecule
  • dihydric - two alcohol groups on the molecule
  • polyhydric - more than 2 alcohol groups on the molecule

Alcohol classifications are based on the number of alcohol groups
alcohol classifications

Solubility

The number of alcohol groups that a molecule has will affect its solubility. As the number of alcohol groups increase on the molecule with the same number of carbons, the solubility in water increases. For example, 1,4-butandiol is more soluble in water than 1-butanol.

1-butanol (above) is less soluble than 1,4-butandiol, because it has fewer alcohol groups
butanol

Another way to think about this is that as the number of carbon atoms increase in an alcohol, the solubility in water decreases. So, 1-octanol with eight carbons per alcohol group is less soluble in water than 1-butanol with four carbons per alcohol group.

Alcohol Functional Group Classification

Alcohols can also be classified based on the carbon to which they are attached.

  • primary - the alcohol is attached to a carbon with two hydrogens
  • secondary - the alcohol is attached to a carbon with one hydrogen
  • tertiary - the alcohol is attached to a carbon atom with no hydrogens

Examples of primary, secondary, and tertiary alcohols
classification of alcohols

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