IUPAC Naming

1 carbon

Meth-

2 carbons

Eth-

3 carbons

Prop-

4 carbons

But-

5 carbons

Pent-

6 carbons

Hex-

7 carbons

Hept-

8 carbons

Oct-

9 carbons

Non-

10 carbons

Dec-

11 carbons

Undec-

12 carbons

Dodec-

How do you choose the parent chain?

• Step 1: Scan for functional groups: Look for groups like -COOH, -OH, -NH2, or carbonyls that dictate the suffix of the molecule and ensure they sit on the main chain.

• Step 2: Find the longest path: Trace all possible continuous carbon pathways from end to end and count the total carbons.

• Step 3: Resolve ties with branches: If two chains tie for the longest carbon count, count how many side branches attach to each; select the one with more branches.

• Step 4: Number the chain: Number your chosen parent chain starting from the end closest to a substituent, double/triple bond, or functional group so that they receive the lowest possible numbers.

Which end do you number the parent chain from?

Number the parent chain starting from the end that gives the substituents the lowest possible numbers (locants).

How are alkyl substituents named?

by taking the name of the parent alkane, removing the -ane ending, and replacing it with -yl

How do you name repeated identical substituents?

• Number the parent chain to give substituents the lowest locants.

• List all locants for identical substituents:

  • same carbon: 2,2-

  • different carbons: 2,4-

• Use prefixes for repeats:

  • 2 = di-

  • 3 = tri-

  • 4 = tetra-

  • 5 = penta-

  • 6 = hexa-

• Punctuation:

  • commas between numbers: 2,3-

  • hyphens between numbers and words: 2,3-dimethyl

  • no spaces

• When alphabetizing, ignore di-, tri-, tetra-, etc.

Example:

3-ethyl-2,2-dimethylpentane

Do di-, tri-, and tetra- count when alphabetizing?

No, you alphabetize by substituent name.

How are different substituents ordered in a name?

List them alphabetically, regardless of their locant numbers.

How are cycloalkanes named?

• Count ring carbons and add cyclo- to the alkane name.

• One substituent: its carbon is automatically C1; don’t write the 1.

• Multiple substituents: number the ring for the lowest set of locants.

• If numbering ties, give C1 to the substituent that comes first alphabetically.

• List substituents alphabetically; ignore di-, tri-, etc.

  • If an attached chain is longer than the ring, the chain is the parent and the ring becomes a cycloalkyl substituent.

How do double and triple bonds change the suffix?

• Double bond: change -ane → -ene

• Triple bond: change -ane → -yne

• Multiple double/triple bonds: use di-, tri-, tetra-, etc.

  • Example: diene, diyne

• Both present: use -en-yne, with ene before yne in the name.

• Give the multiple bond(s) their appropriate locant numbers.

Examples:

propane —> propene

propane —> propyne

pent-1-en-4-yne

What punctuation is used in IUPAC names?

Commas separate numbers; hyphens separate numbers from words; no spaces.