Cyclic Compounds 1 - Cycloalkanes

The molecule forms a cyclic (ring) structure.
Since there is no beginning or end, the numbering is a little different.
The cycle is used to indicate the molecule is ring shaped.

Here is an example of an cyclic compound.


Notice that there 5 carbons all in a ring formation.
Hence the name is :
cyclopentane
The molecular formula is: C5H10

Since cyclic compounds can be difficult to draw, they are represened in a simpler form. This is cyclopentane in symbolic form:

  1. The CORNERS represent the CARBON atoms.
  2. There are 5 corners, showing that there are 5 carbons, hence cyclopentane.
  3. The HYDROGEN atoms are understood to be present.
  4. The molecular formula is: C5H10

As a reminder, pentane is a straight chain:


The molecular formula is: C5H12

Hence cyclopentane and pentane are not isomers. Isomers have the SAME molecular formulae and DIFFERENT structural formulae.

Example 1

chlorocyclopentane
No numbering is required since there is only 1 chlorine atom.
The molecular formula is: C5H9Cl
Example 2

1,3-dichlorocyclopentane
This order of numbering produces smaller numbers.
The molecular formula is: C5H8Cl2
Example 3

1-bromo-3-chlorocyclopentane
There are only two atoms to be numbered. Start in alphabetical order for numbering.
Example 4

(Notice that there are 6 carbons (corners) in the ring... hence cyclohexane)

1-chloro-3-methylcyclohexane
There are only two atoms to be numbered. Start in alphabetical order for numbering.
Example 5

1-bromo-2,4-dichlorocyclohexane
Since you can count either way in a circle, pick the direction that produces lower numbers for the other atoms.
Although you must number in a manner producing the smallest number set, the atoms must still be listed in alphabetical order.
Example 6

2-bromo-1-chloro-3-methylcycloheptane
In either direction, the numbering would be 1,2,3. Then choose choose the chlorine to be 1 due to alphabetic. Remember, in the name, maintain alphabetical order.

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