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3.1: Naming Alkanes

Difficulty Level: At Grade Created by: CK-12
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An alkane is a compound that only contains hydrogens and carbons linked by single bonds. To name an alkane, follow these rules:

1. Identify and name the longest continuous carbon chain, called the parent chain.

The prefix for the name of an alkane will change based on the number of carbons present in the parent chain. These prefixes are as follows:

Add the appropriate prefix to the beginning of “-ane”. The “-ane” signifies that this is a carbon chain with only single bonds, or a saturated carbon chain. For example, a saturated carbon chain with six carbons would have the prefix “hex” added onto “-ane.” This chain would be called hexane.

If there is a functional group present, the name of the organic compound is changed. For example, if there is an alcohol group, the suffix “-anol” replaces the suffix “-ane.”

2. Identify any groups that are attached to the chain.

Some common groups that can be attached to alkanes are “methyl” and “ethyl.” A methyl group is CH3, while ethyl is C2H5.

If there are multiple groups present, name both and put them in alphabetical order. If there are multiple of one group, put a prefix (di, tri, and so on) denoting that there are several groups of the same kind. For example, if there were two “ethyl” groups present on a hexane, it would be known as a diethyl hexane. These prefixes are not considered when alphabetizing the groups. In other words, in a compound with one “ethyl” group and two “methyl” groups, “ethyl” would still come before “dimethyl.”

3. Assign location numbers to the groups.

Add numbers in front of the group name to designate where it is located on the carbon chain. These numbers can be determined by counting carbons. Starting at one of the ends of the carbon chain, count the carbons until you get to the carbon that the group is attached to. This number will go in front of the group name. It is very important to start at the end of the carbon chain that will make the location number as small as possible.

For example,

The parent chain would be hexane. You can also see that there is a methyl group attached. Depending on where you start counting carbons, you could name this molecule either 3-methylhexane or 4-methylhexane. However, only the name with the smallest location number would be correct. This molecule would be correctly named 3-methylhexane.

The format for the nomenclature of alkanes is:





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Feb 23, 2012
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