Hydrocarbons, or compounds made up of a chain of hydrogen and carbon, are the basis of organic chemistry. It is necessary to learn to name them according to the IUPAC nomenclature, or International Union of Pure and Applied Chemistry, which is the currently accepted method for naming hydrocarbon chains.
Steps
Step 1. Know why the rules exist
The IUPAC standards were created to eliminate old names (such as "toluene") and replace them with a consistent system that provides information on the location of substituents (atoms or molecules attached to a hydrocarbon chain).
Step 2. Keep a list of prefixes handy
These prefixes will help you name hydrocarbons. They are based on the number of carbon atoms in the main chain (not all together). For example, CH3-CH3 it would be ethane. Your professor probably doesn't expect you to know prefixes greater than 10; make a note if he or she requests them.
- 1: methyl-
- 2: et-
- 3: prop-
- 4: but-
- 5: pent-
- 6: hex-
- 7: hepta-
- 8: Oct-
- 9: not-
- 10: dec-
Step 3. Practice
Learning the IUPAC system takes practice. Read the following methods to see some examples, then find the links to practice under Sources and Citations at the bottom of the page.
Method 1 of 5: Alkanes
Step 1. Understand what an alkane is
An alkane is a hydrocarbon chain that does not contain double or triple bonds between carbon atoms. The suffix at the end of an alkane should always be - anus.
Step 2. Draw the molecule
You can draw all symbols, or use a skeleton structure. Find out which one your teacher wants you to use, and stick to that.
Step 3. Number the coals on the main chain
The main chain is the longest continuous carbon chain in the molecule. Number it starting from the nearest substituent group. Each substituent will be noted with its numerical position on the chain.
Step 4. Edit the name in alphabetical order
The substituents must be named alphabetically (excluding prefixes such as di-, tri- or tetra-), not in numerical order.
If you have two identical substituents on the hydrocarbon chain, put "di-" before the substituent. Even if they are on the same carbon, write the number twice
Method 2 of 5: Alkenes
Step 1. Know what an alkene is
An alkene is a hydrocarbon chain containing one or more double bonds between carbon atoms, but without triple bonds. The suffix at the end of an alkene should always be - ene.
Step 2. Draw the molecule
Step 3. Find the main chain
The main chain of an alkene must contain double bonds between carbon atoms. Also, it must be numbered starting from the end closest to a carbon-carbon double bond.
Step 4. Note where the double bond is located
In addition to seeing where the substituents are, you also need to see the position of the double bond. Do this so that the lowest number on the double bond is used.
Step 5. Edit the suffix based on the number of double bonds in the main chain
If the chain has two double bonds, its name will end in "-diene". Three is "-triene" and so on.
Step 6. Name the substituents alphabetically
As with alkanes, it is necessary to list the substituents in alphabetical order. Exclude prefixes such as di-, tri- and tetra-.
Method 3 of 5: Alkynes
Step 1. Know what an alkyne is
An alkyne is a hydrocarbon chain containing one or more triple bonds between carbon atoms. The suffix at the end of an alkyne should always be - ino.
Step 2. Draw the molecule
Step 3. Find the main chain
The main chain of an alkyne must contain carbons which are linked with a triple bond. Number it starting from the end closest to a carbon-carbon triple bond.
If you are dealing with a molecule that has both double and triple bonds, start numbering from the end closest to any multiple bonds
Step 4. Note where the triple bond is located
In addition to seeing where the substituents are, it is also necessary to note where the triple bond is. Do this so that the lowest number on the triple bond is used.
If the molecule contains double and triple bonds, these must also be identified
Step 5. Edit the suffix based on the number of triple bonds in the main chain
If the chain has two triple bonds, the name will end in "-diino". Three is "-triino" and so on.
Step 6. Name the substituents alphabetically
As with alkanes and alkenes, it is necessary to list the substituents in alphabetical order. Exclude prefixes such as di-, tri- and delta-.
If the molecule contains double and triple bonds, the double bonds must be named first
Method 4 of 5: Cyclic Hydrocarbons
Step 1. Find out what kind of cyclic hydrocarbon you have
Cyclic hydrocarbons function like non-cyclic hydrocarbons in naming - those that do not contain multiple bonds are cycloalkanes, those with double bonds are cycloalkenes, and those with triple bonds are cycloalkynes. For example, a 6-carbon ring with no multiple bonds is cyclohexane.
Step 2. Know the difference in naming a cyclic hydrocarbon
There are some differences in naming cyclic and non-cyclic hydrocarbons:
- Since all carbon atoms in a cyclic hydrocarbon ring are the same, it is not necessary to use a number if the cyclic hydrocarbon has only one component.
- If the alkyl group attached to the cyclic hydrocarbon is larger or more complex than the ring, the cyclic hydrocarbon can become a main chain substituent.
- If there are two substituents on the ring, they are numbered alphabetically. The first substituent (in alphabetical order) is 1; the next is numbered going clockwise or counterclockwise - whichever is lower for the second substituent.
- If more than two substituents are on the ring, the first in alphabetical order is said to be attached to the first carbon atom. The others are numbered clockwise or counterclockwise - whichever has the lowest numbers.
- Like non-cyclic hydrocarbons, the final molecule is named alphabetically, excluding prefixes such as di-, tri- and tetra-.
Method 5 of 5: Benzene derivatives
Step 1. Understand what a benzene derivative is
A benzene derivative is based on a benzene molecule, C.6H.6, which has three evenly spaced double bonds.
Step 2. Do not use numbering if there is only one substituent
As with other cyclic hydrocarbons, there is no need to use a number if the ring has only one substituent.
Step 3. Learn the conventional names of benzene
You can name the benzene molecule, as you would any other cyclic hydrocarbon, starting in alphabetical order with the first substituent and assigning the numbers by turning. However, there are some special designations for the positions of the substituents on benzene:
- Ortho, or o-: the two substituents are in position 1 and 2.
- Meta, or m-: the two substituents are in position 1 and 3.
- Para, or p-: the two substituents are in position 1 and 4.
Step 4. If the benzene molecule has three substituents, name it as you would a normal cyclic hydrocarbon
Advice
- If there are two possibilities for the longest chain, choose the chain with the most branches. If the two chains have the same number of branches, choose the one that has the first branches. If the two chains are identical in branching, just pick one.
- If a hydrocarbon has an OH (hydroxyl group) in any part of the compound, it becomes an alcohol and is named with the suffix -ol instead of -ane.
- Practice! When you tackle these problems in a test, the professor will likely have designed them so that there is only one right answer. Remember the rules, and follow them step by step.
