Question

Draw structural formulas showing all the isomers of the straight-chain alkyne with eight carbon atoms. Name each isomer.

Short answer

The straight-chain alkyne with eight carbon atoms has the molecular formula C8H14. There are four possible isomers with different placements of the triple bond: 1) 1-Octyne: H-C≡C-C-C-C-C-C-H 2) 2-Octyne: H-C-C≡C-C-C-C-C-H 3) 3-Octyne: H-C-C-C≡C-C-C-C-H 4) 4-Octyne: H-C-C-C-C≡C-C-C-H

Step-by-step solution

Determine the molecular formula of the alkyne

The molecular formula of an alkyne with "n" carbon atoms can be determined using the general formula CnH2n-2. In this case, with eight carbon atoms, the molecular formula is C8H14.

Place the triple bond in different positions

With a straight-chain alkyne with eight carbon atoms, we will have multiple possibilities for placing the triple bond between carbon atoms. We will start with placing the triple bond between carbon 1 and 2, and continue the process by moving the triple bond one carbon forward in each step until we reach the last possible position.

Draw the isomers and name them

i) Structure: H-C≡C-C-C-C-C-C-H Name: 1-Octyne ii) Structure: H-C-C≡C-C-C-C-C-H Name: 2-Octyne iii) Structure: H-C-C-C≡C-C-C-C-H Name: 3-Octyne iv) Structure: H-C-C-C-C≡C-C-C-H Name: 4-Octyne As we see, when we try to place the triple bond between any further carbon atoms, it will just result in the same isomers we've already drawn but flipped. Therefore, the four isomers above are the only ones exist for a straight-chain alkyne with eight carbon atoms.

Key concepts

Alkyne Molecular Formula

Understanding the molecular formula of an alkyne is crucial for grasping the fundamental aspects of these organic compounds characterized by a carbon-carbon triple bond. The general formula for alkynes is given as C_nH_2n-2, indicating that for every 'n' number of carbon atoms, there are '2n-2' hydrogen atoms.

To exemplify, an alkyne with eight carbon atoms would adhere to this formula: C₈H₁₄. This formula helps predict the number of hydrogen atoms present, providing a starting point for drawing structural formulas of the possible isomers for a given alkyne.

Structural Formulas of Isomers

When it comes to illustrating different molecules that share the same molecular formula but differ in their chemical structures, we utilize structural formulas. This is particularly important for isomers—different compounds with the same number and type of atoms. For straight-chain alkyne isomers, the variance lies in where the triple bond is placed along the chain of carbon atoms.

An intricate part of understanding is how subtle alterations in bond placement can lead to different isomers, each with unique physical and chemical properties. This concept forms the basis for exploring the diversity of organic compounds derived from seemingly simple molecular formulas.

Naming Chemical Isomers

The nomenclature of isomers follows specific rules set by the International Union of Pure and Applied Chemistry (IUPAC), ensuring standardized names worldwide. For alkynes, the naming convention includes the position of the triple bond, denoted by the smallest possible number, and the alkyne suffix '-yne'.

For instance, in an eight-carbon alkyne, the four structural isomers mentioned would be named 1-Octyne, 2-Octyne, 3-Octyne, and 4-Octyne respectively. These names tell chemists not only the length of the carbon chain but also the precise position of the triple bond, crucial information for identifying the structure of the compound.

Triple Bond Placement in Alkynes

The placement of the triple bond in an alkyne chain defines the isomer's structure and is a major determiner of its reactivity and physical properties. The bond can move along the straight chain of carbon atoms, but its position is always named with the lowest possible number to ensure consistency in nomenclature.

Starting from the end of the carbon chain that provides the lowest numbering, triple bonds can occupy successive positions to create distinct isomers. After the middle of the chain is reached, no new isomers are formed because the resulting compounds would simply be mirror images of the ones already counted. This concept underlines the importance of triple bond placement when determining isomer count and structure.