3 Naming Alkynes Ws Key | PDF - Free Printable

To name alkynes correctly, we follow these steps:
1. Find the longest carbon chain that contains the triple bond. This determines the base name (e.g., hex- for 6 carbons).
2. Number the chain starting from the end closest to the triple bond. This gives the triple bond the lowest possible number.
3. Identify and locate substituents (branches like methyl or ethyl groups) attached to the main chain.
4. Assemble the name: List substituents in alphabetical order with their position numbers, followed by the base name and the position of the triple bond (ending in -yne).

Here is the step-by-step solution for each structure shown in the worksheet:

1. Top Left Structure
* Chain: The longest chain containing the triple bond has 6 carbons (hex-).
* Numbering: Start from the left to give the triple bond position 1.
* Substituent: There is a methyl group ($CH_3$) at position 3.
* Name: 3-methyl-1-hexyne

2. Top Right Structure
* Chain: The longest chain containing the triple bond has 7 carbons (hept-). Note: You must follow the path through the $CH_2$ group, not the branch.
* Numbering: Start from the right to give the triple bond position 2.
* Substituent: There is an ethyl group ($CH_2CH_3$) at position 4.
* Name: 4-ethyl-2-heptyne

3. Second Row Left Structure
* Chain: The longest chain containing the triple bond has 8 carbons (oct-).
* Numbering: Start from the left to give the triple bond position 3.
* Substituents: There are methyl groups at positions 2, 5, and 6.
* Name: 2,5,6-trimethyl-3-octyne

4. Second Row Right Structure
* Chain: The longest chain containing the triple bond has 7 carbons (hept-).
* Numbering: Start from the right to give the triple bond position 2.
* Substituents: There are methyl groups at positions 3 and 5.
* Name: 3,5-dimethyl-2-heptyne

5. Third Row Left Structure
* Chain: The longest chain containing the triple bond has 8 carbons (oct-).
* Numbering: Start from the right to give the triple bond position 1.
* Substituents: There is an ethyl group at position 3 and a methyl group at position 5.
* Alphabetical Order: Ethyl comes before Methyl.
* Name: 3-ethyl-5-methyl-1-octyne

6. Third Row Right Structure
* Chain: The longest chain containing the triple bond has 7 carbons (hept-).
* Numbering: Start from the right to give the triple bond position 2.
* Substituents: There are methyl groups at positions 3, 5, and 5.
* Name: 3,5,5-trimethyl-2-heptyne

7. Bottom Left Structure
* Chain: The longest chain containing the triple bond has 8 carbons (oct-).
* Numbering: Start from the bottom/left side where the triple bond starts at position 1.
* Substituents: There are two methyl groups at position 3 and one ethyl group at position 5.
* Alphabetical Order: Ethyl comes before Methyl.
* Name: 5-ethyl-3,3-dimethyl-1-octyne

8. Bottom Right Structure
* Chain: The longest chain containing the triple bond has 7 carbons (hept-).
* Numbering: Start from the right to give the triple bond position 2.
* Substituents: There are methyl groups at positions 3 and 5.
* Name: 3,5-dimethyl-2-heptyne

Final Answer:
1. 3-methyl-1-hexyne
2. 4-ethyl-2-heptyne
3. 2,5,6-trimethyl-3-octyne
4. 3,5-dimethyl-2-heptyne
5. 3-ethyl-5-methyl-1-octyne
6. 3,5,5-trimethyl-2-heptyne
7. 5-ethyl-3,3-dimethyl-1-octyne
8. 3,5-dimethyl-2-heptyne