Name to Formula

Figuring out the structural formula starting with the name is done in the same way as it was for alkanes. Most people find this easier that determining the name, so we'll just have one example.

Guidelines

As with the alkanes, start at the end of the name to find out how long the chain is. Then add each of the named additions in the position indicated.

Example

Let's figure out the structural formula for the compound shown here.

1,4-dichloro-3-ethylhexane

The end of the name is hexane so we will start with a six-carbon-atom chain. For convenience, let's number the chain from left to right. Numbering from right to left would be just as correct.

C-C-C-C-C-C
1 2 3 4 5 6

Next, add an ethyl group to the third carbon in the chain. (We could have done the chloros first, instead of the ethyl.)

CH₂CH₃
|
C-C-C-C-C-C
1 2 3 4 5 6

Next, we'll add the two chloro groups, one each to the first and fourth carbons in the chain. For our purposes, it doesn't matter whether the chloros are put above or below the chain. I put them below to keep them out of the way of the ethyl group. When we get to stereoisomers of biochemicals we will have to take such orientation into account.

CH₂CH₃
|
C-C-C-C-C-C

Cl Cl
1 2 3 4 5 6

Next, fill in the necessary hydrogen atoms to complete the molecule. In this example I used a condensed structural formula to keep the Hs from running into the ethyl group. A full structural formula showing a bond to each hydrogen atom could also have been used.

   CH₂CH₃
     |
CH₂-CH₂-CH-CH-CH₂-CH₃
|      |
Cl        Cl

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E-mail instructor: Eden Francis

Clackamas Community College
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