Carbon and its Compounds · Lesson 7 of 13
Nomenclature Of Carbon Compounds
“Carbon compounds finally get names that tell you what is actually inside them.”
• Name simple carbon compounds using carbon-chain length and functional groups. • Use meth-, eth-, prop-, but-, pent- and hex- correctly. • Distinguish prefix and suffix use in naming. • Name simple alkenes and alkynes from unsaturation. • Convert between a simple structural formula and its systematic name.
A systematic name acts like a compact description of a molecule. It tells us the size of the carbon chain and often reveals the functional group or type of carbon-carbon bond. The chapter gives a clear step-by-step naming method.
Carbon-Chain Names
| Carbon Atoms | Root |
|---|---|
| One | Meth- |
| Two | Eth- |
| Three | Prop- |
| Four | But- |
| Five | Pent- |
| Six | Hex- |
A Step-By-Step Naming Method
First identify the number of carbon atoms in the main chain. This gives the basic carbon-chain root. Next identify any functional group. Depending on the group, it is shown by a prefix or suffix. Finally, check whether the carbon chain is saturated or contains a double or triple bond.
Problem
Name CH₃—CH₂—CH₃.
- 1.The structure contains three carbon atoms in the main chain.
- 2.The root for three carbons is prop-.
- 3.All carbon-carbon bonds are single, so the hydrocarbon ending is -ane.
- 4.The name is propane.
Functional Group Prefixes And Suffixes
| Class | Naming Part | Example |
|---|---|---|
| Halo compound | Prefix: chloro-, bromo- | Chloropropane, bromopropane |
| Alcohol | Suffix: -ol | Propanol |
| Aldehyde | Suffix: -al | Propanal |
| Ketone | Suffix: -one | Propanone |
| Carboxylic acid | Suffix: -oic acid | Propanoic acid |
| Alkene | Suffix: -ene | Propene |
| Alkyne | Suffix: -yne | Propyne |
Removing The Final E Before Some Suffixes
If the functional-group suffix begins with a vowel, the final 'e' of the alkane name is removed before adding the suffix. The chapter illustrates this with propane becoming propanone: propane − e = propan, then add -one.
Problem
A three-carbon chain contains a ketone group. Name it.
- 1.Three carbon atoms give the root propane.
- 2.The ketone suffix is -one.
- 3.Remove the final e from propane because the suffix begins with a vowel.
- 4.Propan + one gives propanone.
Naming Unsaturated Carbon Chains
If the carbon chain contains a double bond, replace the ending -ane with -ene. If it contains a triple bond, replace -ane with -yne.
Problem
Name CH₂=CH—CH₃ and HC≡C—CH₃.
- 1.Each structure has three carbon atoms, so both use the root prop-.
- 2.The first contains a double bond, so use -ene: propene.
- 3.The second contains a triple bond, so use -yne: propyne.
From Name To Structure
The process can also be reversed. From 'propanol', identify prop- as a three-carbon chain and -ol as an alcohol group. From 'bromopropane', identify a three-carbon chain and a bromine substituent. The detailed position of the substituent may require structural information when more than one arrangement is possible.
Problem
Interpret propanoic acid.
- 1.Prop- indicates a three-carbon parent chain.
- 2.The ending -oic acid indicates a carboxylic acid functional group.
- 3.The structure therefore contains a three-carbon framework ending in —COOH.
Count carbon atoms, identify the functional group, check for double or triple bonds, then apply the correct prefix or suffix.
Quiz
What root is used for a three-carbon chain?
Which suffix identifies an alcohol?
Which name corresponds to a three-carbon ketone?
Which ending indicates a triple bond?
What happens to the final e in propane when forming propanone?
Practice Problems
- Name CH₃—CH₂—CH₃ using the step-by-step method.
- Name CH₂=CH—CH₃ and explain why the ending changes.
- Name HC≡C—CH₃ and explain how the triple bond affects the name.
- Explain how the names propanol, propanal, propanone and propanoic acid reveal different functional groups.
- Interpret bromopropane in terms of carbon-chain length and substituent.
- Create a table linking meth-, eth-, prop-, but-, pent- and hex- to carbon number and one example each.
Key Takeaways
• Systematic naming begins with the number of carbon atoms in the parent chain. • Functional groups are represented by characteristic prefixes or suffixes. • Alcohol, aldehyde, ketone and carboxylic acid use the endings -ol, -al, -one and -oic acid. • Double and triple bonds are shown by -ene and -yne. • A reliable naming routine is to count carbons, identify functional groups, check unsaturation and then assemble the name.