Nomenclature is one of the very first topics to be introduced in organic chemistry courses. Many students find the process tedious and overwhelming. However, the process of naming molecules is methodic and can be mastered with repeated practice. If you struggle with nomenclature, try the approach below.
===Before you start===
Make sure you memorize the following:
*Functional groups- general structure, IUPAC prefix and suffix.
*Common constituents- name and structure (e.g. t-butyl, neopentyl , sec-butyl, isopropyl and isobutyl)
*Numbering scheme for carbons from 1-12 (e.g. met= 1 carbon, eth=2 carbons etc.)
To make your studying session more efficient, I suggest that you make yourself a “cheat sheet” with these structures and their names. That way, you could easily refer to the structures and names when you practice nomenclature.
===Step 1: Identify functional groups===
At this point, you are ready to tackle your first question. Take a deep breath and look at the molecule. Specifically, identify functional groups within the molecule. Then, find the corresponding IUPAC suffix to use. For example, if your molecule contains a double bond, you should identify the molecule as an alkene, and assign the molecule the suffix “ene”.
If you can’t find a functional group, then the molecule is an alkane, and should have the suffix “ane”.
In the case of molecules with more than one functional group, the more highly oxidized functional group takes priority in naming. For example, if the molecule has a double bond and an alcohol group, the alcohol group takes priority in naming, so the IUPAC name will end with “ol”.
Write down the suffix and continue to the second step.
===Step 2: Identify the main chain===
Your main chain should include as many carbons as possible and as many functional groups as possible (ignore the last part if there are no functional groups in your molecule). Note that your main chain will not necessarily be a straight line. If your chain is cyclic, remember to add the prefix- “cyclo” to the main chain. Assign the appropriate name to the chain- so if for example, your main chain had 8 carbons and an alcohol group, the correct name will be Octanol.
===Step 3: Number the main chain===
IUPAC convention dictates that the constituents and functional group(s) in the molecule receive the lowest number possible. Number the chain from left to right and from right to left, and choose the scheme that has the lowest number for the constituents and the functional groups. Write the numbers down and precede to the last step. You are almost there!
===Step 4: Name the constituents===
Identify and name the constituents. Don’t overlook the constituents you memorized as they often appear in test and homework questions. If there are identical constituents, remember to add di, tri, tetra before the name. List the constituent position, separated by a dash and their name in alphabetical order. Then, list the name of the main chain. For example, your finished name may be 1,1 dimethyl 2, chlorobutane.
With regular practice, this approach should become second-nature. Good luck!