Question

Draw the structural formula for \(n\)-octyne. How many isomers are possible by moving only the position of the triple bond?

Short answer

n-Octyne has a straight-chain structure with eight carbon atoms and a triple bond between the first and second carbon atoms. There are 6 possible isomers by moving the location of the triple bond along the chain without counting the position of the first isomer (n-octyne itself).

Step-by-step solution

Understanding the Compound Name

The compound's name, 'n-octyne', indicates a carbon chain with eight carbons (oct-), and a triple bond (-yne). The 'n-' prefix suggests that the compound is a straight-chain (normal) alkene without any branching.

Drawing the Primary Structure of n-Octyne

Draw a straight chain of eight carbon atoms. Then add a triple bond between the first and second carbons because the 'n-' prefix indicates that the triple bond starts at the first carbon in a straight-chain molecule.

Completing the Structural Formula

Add hydrogen atoms to each carbon atom so that each carbon atom makes four bonds in total. The carbons involved in the triple bond will have fewer hydrogens.

Identifying Isomers Based on Triple Bond Position

To find the isomers, move the position of the triple bond along the carbon chain. Start with the triple bond between carbons 1 and 2 for the first isomer. Then, move the triple bond to between carbons 2 and 3 for the second isomer, and continue moving the triple bond one carbon down the chain each time until it can't be moved further without leaving the chain or creating a repeat of a previous structure.

Counting the Isomers

Count each distinct compound created by moving the triple bond along the carbon chain. These are the isomers of n-octyne based on the position of the triple bond.

Key concepts

Alkyne Isomers

Alkynes are hydrocarbons with at least one carbon-carbon triple bond. These molecules are interesting in organic chemistry because of their unique properties and reactivities. An important aspect to understand is the concept of isomerism in alkynes.
Isomers are compounds with the same molecular formula but different structural configurations. For alkynes, this could mean the difference in the position of the triple bond, the length of the carbon chain, or branching patterns. This diversity arises because carbon atoms can form chains of varying lengths and shapes, leading to numerous possibilities.
For example, when considering n-octyne, an alkyne with eight carbon atoms, moving the triple bond along the chain changes the molecule's physical and chemical properties, hence creating different isomers. The ability to form multiple isomers greatly increases the versatility of alkynes in synthesizing a wide range of organic compounds.

Organic Chemistry Nomenclature

The nomenclature of organic compounds is a systematic method of naming organic chemical substances as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It provides consistency and clarity in the communication of organic chemistry.
For example, the 'n' in 'n-octyne' stands for 'normal', indicating that the compound has a straight, unbranched chain of carbon atoms. The 'oct' signifies the presence of eight carbon atoms, while the suffix '-yne' denotes the existence of a triple bond within the molecule. The number preceding 'octyne', if any, would indicate the exact position of the triple bond; however, lacking such a number suggests the triple bond starts at the first carbon atom.
Understanding these naming conventions allows for the systematic drawing and identification of organic chemical structures, from simple hydrocarbons to complex biomolecules. It is crucial for students to grasp these principles in order to communicate effectively and understand the literature in organic chemistry.

Drawing Structural Isomers

Drawing structural isomers in organic chemistry is an essential skill, allowing students to visualize different arrangements of atoms that constitute a molecule. It involves understanding how atoms can connect in various ways to form distinct molecular structures.
To draw isomers of a compound like n-octyne, one starts by sketching the longest carbon chain. Then, the triple bond's location is varied along this chain. Placement at the chain's beginning produces the first isomer, and subsequent isomers are drawn by moving the triple bond one carbon atom at a time towards the opposite end. This process is repeated until all the unique configurations, which correspond to different isomers, have been depicted.
While practicing, it's important to remember that each carbon must have four bonds and the molecular formula must remain consistent. Through this exercise, students gain a deeper understanding of structural variations in molecules, which is fundamental in learning organic chemistry.