Naming Organic Compounds: A Guide for SCH4U Course
Naming Alkanes with and without Branches
Alkanes are hydrocarbons with only single bonds. The general formula for alkanes is \(C_nH_{2n+2}\).
Unbranched alkanes are named based on the number of carbon atoms in the chain: Methane (1 carbon), Ethane (2 carbons), Propane (3 carbons), Butane (4 carbons), Pentane (5 carbons), Hexane (6 carbons), Heptane (7 carbons), Octane (8 carbons), Nonane (9 carbons), Decane (10 carbons).
For branched alkanes,
1) identify the longest continuous chain of carbon atoms. This is your parent chain.
2) Name the branches (alkyl groups) based on the number of carbons they contain (methyl for 1, ethyl for 2, propyl for 3, etc.).
3) Number the carbons in the parent chain from the end nearest a branch.
4) Assign a number to each branch according to the carbon it's attached to in the parent chain.
5) If there are multiple branches of the same type, use di-, tri-, tetra-, etc. to indicate this.
6) Write the name as a single word, using hyphens to separate numbers and commas to separate multiple numbers.
Example: 4-ethyl-2,2-dimethylheptane
Naming Alkanes with More Than One Alkyl Groups
If there are different types of alkyl groups, list them in alphabetical order. If there are two or more of the same alkyl group, use prefixes (di-, tri-, etc.) and list them based on the first point of difference.
Example: 4-ethyl-3,3-dimethyl-5-propyloctane
Naming Alkenes with and without Branches
Alkenes are hydrocarbons with at least one carbon-carbon double bond. The general formula for alkenes is \(C_nH_{2n}\).
The rules for naming alkenes are similar to those for alkanes, but with a few differences: The parent chain is the longest chain that includes the double bond. The parent chain is numbered from the end nearest the double bond. The position of the double bond is indicated by the lower of the two numbers of the carbons involved in the bond. The suffix "-ene" is used instead of "-ane".
Example: 3-methyl-2-pentene
Naming Alkenes with More Than One Alkyl Groups
The rules are the same as for alkanes with multiple alkyl groups, but with the "-ene" suffix and numbering to indicate the position of the double bond.
Example: 4-ethyl-2,2-dimethyl-3-heptene
Naming Alkynes with and without Branches
Alkynes are hydrocarbons with at least one carbon-carbon triple bond. The general formula for alkynes is \(C_nH_{2n-2}\).
The rules for naming alkynes are similar to those for alkenes, but with the suffix "-yne" instead of "-ene".
Example: 2-pentyne
Naming Alkynes with More Than One Alkyl Groups
The rules are the same as for alkenes with multiple alkyl groups, but with the "-yne" suffix and numbering to indicate the position of the triple bond.
Example: 4-ethyl-2,2-dimethyl-3-heptyne