Straight-Chain Acyclic Hydrocarbons

1. The naming of organic compounds is based on the parent hydrocarbon they derived from. The number of carbon atoms in hydrocarbons is represented by stem names.

Number of carbon atoms	Stem name		Number of carbon atoms	Stem name
	Meth- Eth- Prop- But- Pent-			Hex- Hept- Oct- Non- Dec-

2. (a) The suffix ‘ane’ is used for saturated hydrocarbons.

e.g. CH₃ − CH₃ ethane
CH₃CH₂ − CH₃ propane

(b) The suffix ‘ene’ is used for unsaturated hydrocarbons with a double bond.

e.g. CH₂ = CH₂ ethene
CH₃CH = CH₂ propene

(c) The suffix ‘yne’ is used for unsaturated hydrocarbons with a triple bond.

e.g. CH º CH ethyne
CH₃CH º CH propyne

3. The lowest possible number is assigned to the carbon atoms of the multiple bond.

The number is written before the suffix to indicate the position of the carbon atom of the multiple bond

e.g. CH₃CH₂CH = CH₂ but-1-ene (not but-3-ene)

CH₃C º CCH₂CH₃ pent-2-yne (not pent-3-yne)

4. If a compound contains more than one double or triple bond, the prefixes like ‘di-’, ‘tri-’, are used to indicate its number of occurrence. An ‘a’ is added to the corresponding stem name.

e.g. CH₃CH₂CH = CHCH = CH₂ hexa-1,3-diene

5. If a double or triple bond is not named in the ending of a name, the suffix ‘-en-’ and ‘-yn-’ are used respectively in the name.

e.g. CH₂ = CHOH ethenol

6. The geometric isomers of an alkene are specified by the word of ‘ cis -’ or ‘ trans -’ before their names. e.g.

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