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Naming Alcohols Using IUPAC Nomenclature

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson will help you understand how to apply IUPAC naming conventions to alcohols. We'll first review what primary, secondary and tertiary alcohols are, and then look at IUPAC naming conventions. Lastly, we'll look at naming some examples.

What's In a Name?

All of this naming in organic chemistry might seem a bit 'extra'. Why bother going through the trouble of having a specific naming system? In everyday life, we use different names for the same thing. Some people might refer to a carbonated drink as 'soda', while others might say 'pop'. Since carbonated drinks are a relatively simple subject, this doesn't pose much of a problem.

However, when we are talking about compounds in organic chemistry, the compounds can be quite complex, and difficult to describe without a clear, concise naming system. The International Union of Pure and Applied Chemistry (IUPAC) provides nomenclature guidelines for all types of compounds. This gives scientists a clear way to communicate about what chemicals are being used in their experiments and manufacturing. Today, we'll be looking at the IUPAC naming conventions for alcohols.

Types of Alcohols

What is an alcohol anyway? You might be familiar with alcohol in wine or beer, or maybe as an antiseptic. But, in organic chemistry, an alcohol is any alkyl, or carbon based compound, with a hydroxide functional group, that's an oxygen and hydrogen bound together.

There are three types of alcohols: primary, secondary and tertiary. Primary alcohols are bound to a primary carbon, or a carbon atom bound to one other group. Secondary alcohols are bound to secondary carbons, or carbons bound to two groups. Tertiary alcohols are alcohols bound to a tertiary carbon, or a carbon bound to three groups.

IUPAC Naming Rules

The functional group is the center of reactivity for an alkyl molecule. In alcohols, the alcohol group is the functional group, and thus the alkyl is named as such. To name any alcohol, we first need to review how to name alkyl chains. Let's review the table here:

Number of Carbons Name
1 Methane
2 Ethane
3 Propane
4 Butane
5 Pentane
6 Hexane
7 Heptane
8 Octane
9 Nonane
10 Decane

Naming Alcohols

  • First count the longest carbon chain from the lowest position of the alcohol. You may need to count from right to left at times and left to right at other times. Carbons will appear as the letter 'C', or sometimes as intersections between straight lines depending on the type of diagram.
  • After counting the number of carbons, choose the matching alkane name. Then drop the 'e' at the end of the name and add the suffix 'ol' to name it as an alcohol.
  • Use a number in the beginning of the name as a prefix to indicate which carbon the alcohol is branched from.
  • Include additional substituent groups, or alkyl groups, branching from the main hydrocarbon chain as well. List substituents, with number prefixes indicating their position, in alphabetical order prior to naming the alcohol.

Examples

Primary Alcohol

Now, let's look at an example of naming a primary alcohol.

An example of a primary alcohol
primary alcohol

To start, we find the longest carbon chain attached to the alcohol group. This one is only two carbons long, so the alkane name is ethane. Now, we replace the 'e' with 'ol' and we have the IUPAC name, 1-ethanol, or simply ethanol. The '1' indicates that the alcohol group is attached to the first carbon, but if no number is included this information is assumed.

Now, let's look at how to name alcohols with additional substituents.

An alcohol with additional substituents
primary alcohol

Start by finding the longest carbon chain that includes the alcohol group. In this example each angle, or intersection between lines, is one carbon atom, so the chain is three carbons long. The base alkane name then is propane.

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