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naming alkanes 1 2 > tutorials > home      

Applying the Rules

Now try applying these rules to name the following molecule (it's not as hard as it might seem).

What am I called?

Take it step by step as outlined above.

1) Find the longest carbon chain in the molecule. First, begin by finding the parent chain in the molecule--that is, the longest possible chain of connecting carbons. Note that the parent chain is not necessarily the chain that simply follows from left to right. For example, if you were to count the number of carbons directly from left to right in this molecule you would get 7 carbons. This is not the parent chain, however! If you start at the left and then count up where the molecule branches, you find that there are 8 carbons by taking this route. This is is the longest chain (dont be fooled by professors hiding carbons in branches), and thus the parent chain is octane (see table above).

2) Number the parent chain. The second step is to number the carbons in the parent chain starting at the end closest to the first substituent. It is important to number the molecule from the correct end (in other words, in this example do you number the alkane from right to left or left to right). Following this rule, on this molecule you number from right to left, as the 2-carbon substituent is closer to that end.

Numbered Right

Numbered Wrong
Correct Numbering Incorrect Numbering

3. Name all the substituents. You then identify the names of the substituents. In this case, the only substituent is a 2 carbon group at the number 4 carbon. This is an ethyl group.

4. Put the substituents in alphabetical order. The next step is to put the substituents in alphabetical order (ie. ethyl before methyl) but since there is only one substituent this is unnecessary.

5. Locate the substituent on the parent change by giving it a number. Thus, the proper nomenclature of this alkane is 4-ethyloctane. Note that a dash is used to separate the number from the substituent.

Now you try naming one!

1. What is the IUPAC name of the following:

IUPAC Nomenclature

Score =
Correct answer:


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