Everything Science Grade 12

CHAPTER 1. ORGANICMOLECULES 1.7

Example 7: Naming the alkenes

QUESTION

Give the IUPAC name for the following compound:

H C(1)

H

C(2)

CH 2

CH 3

C(3)

H

C(4)

H

H

SOLUTION

Step 1 : Identify the functionalgroup

The compound is an alkene and will have the suffix -ene. There

is a double bond between the first and secondcarbons and also

between the third and forth carbons. The organic compound is

therefore a ’diene’.

Step 2 : Find the longest carbonchain and number the carbon atoms

There are four carbon atoms in the longest chainand so the prefix

for this compound will be ’but’. The carbon atoms are numbered

1 to 4 in the diagram above. Remember thatthe main carbon

chain must contain boththe double bonds.

Step 3 : Look for any branchedgroups, name them andgive their posi-

tion on the carbon chain

There is an ethyl groupon the second carbon.

Step 4 : Name the compound

The name of this compound is 2-ethyl-but-1,3-diene.

Exercise 1 - 5

Give the IUPAC name for each of the following alkenes:

1. CH 2 CHCH 2 CH 2 CH 3