Problem 56 - Introductory Chemistry Atoms First

Question

What endings are added to the root alk- to name hydrocarbons containing all \(\mathrm{C}-\mathrm{C}\) single bonds, hydrocarbons containing one or more \(\mathrm{C}=\mathrm{C}\) double bonds, and hydrocarbons containing one or more \(\mathrm{C} \equiv \mathrm{C}\) triple bonds?

Step-by-Step Solution

Answer

For the root "alk-", the endings added to name hydrocarbons are "-ane" for those containing all \(\mathrm{C}-\mathrm{C}\) single bonds (alkanes), "-ene" for those containing one or more \(\mathrm{C}=\mathrm{C}\) double bonds (alkenes), and "-yne" for those containing one or more \(\mathrm{C} \equiv \mathrm{C}\) triple bonds (alkynes).

Step 1: Name hydrocarbons with all single bonds

To name a hydrocarbon with all single bonds (alkanes), we use the prefix "alk" and add the ending "-ane" to the root. These hydrocarbons follow the general formula \(\mathrm{C}_n\mathrm{H}_{2n+2}\), where n represents the number of carbon atoms in the molecule. For example, methane (\(\mathrm{CH}_4\)), ethane (\(\mathrm{C}_2\mathrm{H}_6\)), and propane (\(\mathrm{C}_3\mathrm{H}_8\)) are all alkanes with no double or triple bonds.

Step 2: Name hydrocarbons with one or more double bonds

To name a hydrocarbon containing one or more carbon-carbon double bonds (alkenes), we add the ending "-ene" to the root "alk". Alkenes follow the general formula \(\mathrm{C}_n\mathrm{H}_{2n}\), where n represents the number of carbon atoms in the molecule. Additionally, we need to indicate the position of the double bond in the hydrocarbon chain using a number. The number should be as low as possible, and it corresponds to the first carbon of the double bond. For example, ethene (\(\mathrm{C}_2\mathrm{H}_4\)), propene (\(\mathrm{C}_3\mathrm{H}_6\)), and butene with a double bond between carbons 1 and 2 (\(\mathrm{C}_4\mathrm{H}_8\)) are examples of alkenes.

Step 3: Name hydrocarbons with one or more triple bonds

To name a hydrocarbon containing one or more carbon-carbon triple bonds (alkynes), we add the ending "-yne" to the root "alk". Alkynes follow the general formula \(\mathrm{C}_n\mathrm{H}_{2n-2}\), where n represents the number of carbon atoms in the molecule. Similar to alkenes, we need to indicate the position of the triple bond in the hydrocarbon chain using a number. The number should be as low as possible, and it corresponds to the first carbon of the triple bond. For example, ethyne (\(\mathrm{C}_2\mathrm{H}_2\)), propyne (\(\mathrm{C}_3\mathrm{H}_4\)), and butyne with a triple bond between carbons 1 and 2 (\(\mathrm{C}_4\mathrm{H}_6\)) are examples of alkynes. In conclusion, for the root "alk-", we add the endings "-ane" for hydrocarbons containing all single bonds, "-ene" for hydrocarbons containing one or more double bonds, and "-yne" for hydrocarbons containing one or more triple bonds.

Key Concepts

Alkanes

Alkanes are the simplest type of hydrocarbons, consisting only of carbon (C) and hydrogen (H) atoms. They contain only single bonds between carbon atoms. This results in a saturated molecule, meaning it has the maximum number of hydrogen atoms attached.

When naming alkanes, the suffix "-ane" is added to the root word, which typically indicates the number of carbon atoms in the molecule.

• For one carbon, use "meth-" resulting in "methane" (\(\mathrm{CH}_4\)).
• For two carbons, use "eth-" resulting in "ethane" (\(\mathrm{C}_2\mathrm{H}_6\)).
• For three carbons, use "prop-" resulting in "propane" (\(\mathrm{C}_3\mathrm{H}_8\)).

Each name corresponds to the formula \(\mathrm{C}_n\mathrm{H}_{2n+2}\), where "n" is the number of carbon atoms. Their structure ensures a stable configuration, making alkanes relatively unreactive compared to other hydrocarbons. However, they are excellent fuels and can undergo combustion.

Alkenes

Alkenes are hydrocarbons characterized by at least one double bond between carbon atoms (\(\mathrm{C}=\mathrm{C}\)). This introduces a degree of unsaturation into the molecule.

The ending "-ene" is used for alkenes, and care must be taken in naming them to indicate the position of the double bond. This is important in ensuring the clarity and precision of hydrocarbon nomenclature.

• Ethene, or ethylene (\(\mathrm{C}_2\mathrm{H}_4\)), is the simplest alkene, consisting of two carbon atoms with a double bond.
• Propene (\(\mathrm{C}_3\mathrm{H}_6\)) follows, with a double bond between the first and second carbon in the chain.

The general formula for alkenes is \(\mathrm{C}_n\mathrm{H}_{2n}\), where "n" indicates the number of carbon atoms. This formula reflects the reduced hydrogen atoms due to the presence of a double bond. Because of this, alkenes are generally more reactive than alkanes, participating in addition reactions.

Alkynes

Alkynes are hydrocarbons that contain at least one triple bond (\(\mathrm{C}\equiv\mathrm{C}\)) between carbon atoms, contributing further to the molecule's unsaturation.

The suffix "-yne" denotes alkynes in the hydrocarbon nomenclature system, and the location of the triple bond is critical in their naming process.

• Ethyne, also known as acetylene (\(\mathrm{C}_2\mathrm{H}_2\)), is the simplest example with a triple bond.
• Propyne (\(\mathrm{C}_3\mathrm{H}_4\)) has a triple bond between the first and second carbon atoms of its carbon chain.

The general formula for alkynes is \(\mathrm{C}_n\mathrm{H}_{2n-2}\), where "n" represents the number of carbon atoms. The formula indicates fewer hydrogen atoms due to the triple bond. Alkynes are typically more reactive than both alkanes and alkenes, participating in various addition and substitution reactions.