Question #268a8

A nice example is malonic acid. It is a three-carbon dicarboxylic acid.

Because it is a three-carbon compound, and since there are no #"C"-"C"# double or triple bonds, we can use "propane-" as the parent name.

Now, since there are two carboxyl groups, we use di to indicate that, and oic acid to indicate that they are carboxyl groups.

Since this compound is symmetrical, we don't need to mention the positions of the carboxyl groups.

(Though we could call it propane-1,3-dioic acid, it can be confused with propane-1,3-dicarboxylic acid, which is NOT the same thing, so I tend to avoid that.)

So, malonic acid is also called propanedioic acid.

A more difficult one is citric acid, which is a five-carbon tricarboxylic acid.

In cases like this, we can use the carboxy term for the carboxyl substituent, and a hydroxy term for the hydroxyl substituent. Those are on carbon-3.

Because it is a five-carbon main chain, and since there are no #"C"-"C"# double or triple bonds, we can use "pentane-" as the parent name.

Also, the nice thing about this compound is that it's symmetrical too. So, we have two ways we can name it this:

3-carboxy-3-hydroxypentane-1,5-dioic acid

to be most accurate, or

3-carboxy-3-hydroxypentanedioic acid

which is OK in this case, since it just so happens that the central carbon has the carboxyl and hydroxyl groups, and people can figure out the structure based on its symmetry.