Summary
Highlights
Alkenes are hydrocarbons with at least one double bond. The suffix 'ene' is used to denote the presence of a double bond. The longest carbon chain must be identified, and numbering starts from the end that gives the double bond the lowest possible number, even if other substituents would receive lower numbers from the other direction. For example, 4,4-dimethyl-1-pentene indicates two methyl groups on carbon 4 and a double bond starting at carbon 1 in a five-carbon chain.
Alkynes are hydrocarbons with at least one triple carbon-carbon bond. Carbon atoms participating in a triple bond are sp hybridized and exhibit linear molecular geometry, so they must be drawn linearly. Similar to alkenes, the parent chain is numbered to give the triple bond the lowest possible number. For instance, 6-fluoro-3-heptyne signifies a fluorine atom on carbon 6 and a triple bond starting at carbon 3 in a seven-carbon chain, drawn with the correct linear geometry around the triple bond.
When a molecule contains multiple functional groups, there is an order of prioritization for naming. The hydroxyl group takes the highest priority, followed by an alkyne (triple bond), then an alkene (double bond), and finally alkyl groups and halogens, which have equal priority. The functional group with the highest priority determines the direction of numbering the parent chain and influences the suffix of the name.
For molecules with multiple functional groups, such as an alcohol and an alkene, the highest priority group dictates the numbering. Substituents like halogens and alkyl groups are listed first alphabetically, followed by the functional groups that modify the suffix of the molecule. For example, 5-chloro-3-ethyl-4-methyl-3-hepten-1-ol indicates a seven-carbon chain with a hydroxyl group at carbon 1 (prioritized), a double bond starting at carbon 3, and chloro, ethyl, and methyl substituents.