Question

How is the root name of an alkane modified to indicate that a given hydrocarbon contains a double or triple bond in its longest continuous chain?

Short answer

To modify the root name of an alkane to indicate the presence of a double or triple bond in the longest continuous chain, change the "-ane" suffix to "-ene" for a double bond or "-yne" for a triple bond. Additionally, include the position of the bond in the name using the lowest numbered carbon atom involved in the bond. For example, 1-Butene for a double bond and 1-Butyne for a triple bond in a four-carbon chain.

Step-by-step solution

IUPAC Nomenclature for Alkanes, Alkenes, and Alkynes

The International Union of Pure and Applied Chemistry (IUPAC) provides a standardized system for naming organic compounds. In this system, the root name of a hydrocarbon is determined by the total number of carbon atoms present in the longest continuous chain. The root name for an alkane (containing only single bonds) is modified to indicate the presence of a double or triple bond in the chain.

Naming Alkenes

When a hydrocarbon contains a carbon-carbon double bond, it is called an alkene. To indicate the presence of a double bond in the longest continuous chain, you need to modify the root name by changing the "-ane" ending to "-ene". Also, you must include the position of the double bond in the name, which will be indicated by a number representing the carbon atom with the lowest number to which the double bond is attached. For example, if a hydrocarbon with four carbon atoms has a double bond between the first and second carbons, its name would be: 1-Butene.

Naming Alkynes

Similarly, when a hydrocarbon contains a carbon-carbon triple bond, it is called an alkyne. To indicate the presence of a triple bond in the longest continuous chain, you must change the alkane's root from "-ane" to "-yne". As with alkenes, you must include the position of the triple bond in the name, represented by a number indicating the carbon atom with the lowest number to which the triple bond is attached. For example, if a hydrocarbon with four carbon atoms has a triple bond between the first and second carbons, its name would be: 1-Butyne. In summary, to modify the root name of an alkane to indicate the presence of a double or triple bond in the longest continuous chain, change the "-ane" suffix to "-ene" or "-yne", and include the position of the bond in the name using the lowest numbered carbon atom involved in the bond.