Naming Butyls

What does n-, s-, t- Mean?

The butyl functional group consists of four carbon atoms. These four atoms can be arranged in four different bond configurations when attached to a molecule. Each arrangement has its own name to distinguish the different molecules they form. These names are: n-butyl, s-butyl, t-butyl and isobutyl.

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n-Butyl Functional Group

n-Butyl Chemical Structure
This is the chemical structure of the n-butyl functional group. Todd Helmenstine

The first form is the n-butyl group. It consists of all four carbon atoms forming a chain and the rest of the molecule attaches at the first carbon.

The n- stands for 'normal'. In common names, the molecule would have n-butyl added to the molecule name. In systematic names, n-butyl would have butyl added to the molecule name.

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s-Butyl Functional Group

s-Butyl Chemical Structure
This is the chemical structure of the s-butyl functional group. Todd Helmenstine

The second form is the same chain arrangement of carbon atoms, but the rest of the molecule attaches at the second carbon in the chain.

The s- stands for secondary since it attaches to the secondary carbon in the chain. It is also often labelled as sec-butyl in common names.

For systematic names, s-butyl is slightly more complicated. The longest chain at the point of connection is a propyl formed by carbons 2,3 and 4. Carbon 1 forms a methyl group, so the systematic name for s-butyl would be methylpropyl.

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t-Butyl Functional Group

t-Butyl Chemical Structure
This is the chemical structure of the t-buytl functional group. Todd Helmenstine

The third form has three of the carbons single bonded to a center fourth carbon and the rest of the molecule is attached to the center carbon. This configuration is called t-butyl or tert-butyl in common names.

For systematic names, the longest chain is formed by carbons 2 and 1. Two carbon chains form an ethyl group. The other two carbons are both methyl groups attached at the beginning point of the ethyl group. Two methyls equals one dimethyl. Therefore, t-butyl is 1,1-dimethylethyl in systematic names.

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Isobutyl Functional Group

Isobutyl Chemical Structure
This is the chemical structure of the isobutyl functional group. Todd Helmenstine

The final form has the same carbon arrangement as t-butyl but the attachment point is at one of the ends instead of the center, common carbon. This arrangement is known as isobutyl in common names.

In systematic names, the longest chain is a propyl group formed by carbons 1, 2 and 3. Carbon 4 is a methyl group attached to the second carbon in the propyl group. This means isobutyl would be 2-methylpropyl in systematic names.