|Chapter Eleven, Section Two|
I. ALKANES AND ALKYL HALIDES
The International Union of Pure and Applied Chemistry (IUPAC) has established guidelines for naming compounds so that people from all over the world can communicate with each other regarding chemical compounds. Certainly we would have chaos if everyone could call any chemical compound whatever seemed good to them. There are still some compounds that are called by their "common" names (such as aspirin) and we just have to live with that.
Here are some rules to guide you in the naming process:
The following compound illustrates all of the above (except the common name)
We note the parent compound is pentane and then we use the other rules to arrive at the name
Easy!! Again, a little practice should have you naming such compounds easily. Do note the examples in your book illustrating that the main chain does not have to be in a strict left to right straight line. The main chain can go up and down, zig or zag, or whatever. The following compound is the same as the one above. Study the two until you are convinced that they are the same.
Carbon atoms can also be connected to each other in a ring structure. The naming of the ring structures is rather straightforward. We just put the prefix "cyclo" in front of the appropriate name for the number of carbon atoms involved in the ring:
Now when substituents are added to the rings the names are also rather straightforward. The addition of a single group, such as methyl, requires no numbers of course because all positions on a ring are equivalent. Everyone then knows that methylcyclobutane is
However, if another substituent is added we need to be more specific about exactly where it is located on the ring. We follow the IUPAC rules and specify that we must end up with the lowest numbers involving the substitutions. Consider the following compound for example,
We start at one methyl group and we could call this either 1,4-dimethylcyclobutane or 1,2- dimethylcyclobutane. Using the smallest numbers rule, we call this 1,2 dimethylcyclobutane. A little practice with this nomenclature should allow you to name such compounds easily. You should also be familiar with the very condensed structures that look like stick and ring drawings as shown above.
After you have studied this material and practiced some problems, take quiz two. If you score at least 80 on the test then you are ready to continue to the next section.
Web Author: Dr. Leon L. Combs
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