Naming Alkanes

Explanation: 

Alkanes is a family of molecules that contains C-C single bonds. Alkanes are considered saturated molecules because they contain the maximum amount of hydrogens per carbon.

Generally students taking organic chemistry learn how to name alkanes in the very beginning of their course and are usually tested on it on the first exam.

Naming Alkanes

1. Find the parent chain. This is the longest continuous carbon chain. Name the parent chain using the prefix signifying how many carbons are in the chain and end the name in "ane." For example: propane, butane, pentane.

Number of Carbons                Prefix

            1                              meth

            2                              eth

            3                              prop

            4                              but

            5                              pent

            6                              hex

            7                              hept

            8                              oct

            9                              non

            10                            dec

            11                            undec

2. Number the carbons in the parent chain starting from the carbon closest to the first substituent/branch point (substituents are groups that are not a part of the parent chain.

3. Name substituents by putting a number in front, representing the carbon your substituent is attached to.

Carbon substituents will have an ending of "yl". For example: CH3- methyl, CH3CH2 - ethyl, CH3CH2CH2- propyl

Halogen substituents will end in "o". For example: Br - bromo, Cl - chloro, I - iodo

4. If there are identical substituents, use prefixes di (2), tri(3), tetra(4) and don't forget to still give number to each substituent. For example: 2,3- dimethyl or 2,2,2- tribromo

5. Write the full name by first putting substituents in alphabetical order (prefixes don't count for alphabetical order), followed by the name of the parent chain.

Special Situations:

1. What if 2 substituents are equally close to both ends of the chain? Where do I start numbering?

You should start numbering from the end that is closest to the substituent that takes alphabetical priority.

2. What if there are two possible or more possible parent chains? Choose the one with the most substituents.

Practice Problems

Naming Cycloalkanes

 

Naming cycloalkanes is very similar to naming alkanes. Here are some extra points to pay attention to:

1. Count the number of carbons in the ring. Name the ring using the prefix signifying how many carbons are in it starting with "cycle" and ending in "ane." For example: cyclopropane, cyclobutane, cyclopentane.

2. Number the carbons in the ring starting from the carbon that is attached to the substituent.  If two or more substituents are present, begin numbering at the group that has alphabetical priority and proceed around the ring so as to give the second substituent the lowest number.

Note: 

If your molecule contains both a ring and an alkyl substituent, count the number of carbons in the ring and the number of carbons in the continuous substituent chain. If there are more carbons in the ring, name as above. If there are more carbons in the chain, the ring becomes a substituent and is named as cyclo____yl. For example: 2-cyclopropyldecane.