Naming Organic Compounds Tutorial for Alkanes and Alkenes

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As an organic chemistry student you will be expected to name simple molecules following an IUPAC system, as well as be able to draw molecules from their given nomenclature. In this article I will give you a tutorial for naming simple, straight-chain organic compounds

The names of organic molecules, like the names of human beings, follows a formulaic structure.

Let’s take the name John Doe for example. We have a first name of John and a last name of Doe. This is typically enough to identify the person in question (assuming you replace John and Doe with real names)

When naming organic compounds you want to identify the longest carbon chain as your parent chain. You will then assign this molecule a first name referring to the number of carbons present, and a last name referring to the type of chain in question in regards to its hybridization or carbon to carbon pi bonds

The first names referring to the number of carbons are as follows

1. meth
2. eth
3. prop
4. but
5. pent
6. hex
7. hept
8. oct
9. non
10. dec

The last name refers to the type of chain in regards to single, double, or triple as follows

Single bonds only: ane

1 or more double bonds: ene

1 or more triple bonds: yne

However, unlike human names, molecular nomenclature is combined so that there is no space between the first and last name

Let’s take a look at a number of examples

CH4

This molecule tends to throw students off because we don’t have a continuous chain and therefor do not have the option for double or triple bonds

But the name is simple to find if you follow the naming system

Since we have just one carbon in the chain we get meth

Since we don’t have the potential for double or triple bonds we resort to the single bond last name of ane

putting the name together we have

meth + ane = methane

Now let’s try this with a longer chain

CH3-CH2=CH3

Notice that the parent chain has a total of 3 carbons. This gives us a first name of prop

Next you look for the bonds connecting the carbon atoms. While we do have a single bond between the leftmost and middle carbon atoms, we also have a double bond between the rightmost and middle carbon. The fact that there is a single double bond present gives us a last name of ene

In longer molecules you have to specify the carbon number where the pi bond originates, however in this case, since the pi bond is higher priority you are forced to count from the right. This implies a number 1

Putting this together we get as follows:

prop + ene = propene

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