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Cyclic Compounds Have Their Own Rules

Learn the rules for naming cyclic compounds in organic chemistry. Check out Dr. B's latest blog post for crystal-clear explanations and examples.

There are many rings in organic chemistry and the basic IUPAC for cycloalkanes are the basis for naming them. The basic rules change somewhat for cycloalkanes:

  1. The parent is the ring. Add the prefix cyclo- to the corresponding alkane name with the same number of carbons.
  2. Identify and put the substituents in alphabetical order in front of the parent.
  3. Number to give the lowest combination of numbers.

The molecule below has a cyclohexane parent. The substituents go in alphabetical order so this is an ethyl isopropyl methylcyclohexane. But where are the substituents? Number around the right in both directions to give the 2 lowest possible schemes. 1,2,4 beats 1,3,4 at the 2nd numbers (1st point of difference) so this is a 2-ethyl-4-isopropyl-1-methylcylcohexane.

So you can see it’s the same logical process every time. We find the parent, name the substituents and number with the lowest combination of numbers. For more detailed rules, sample problems and practice problems go to Unit 3.

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