Question

The number of linear carbon atoms in hexyne molecule is (1) 2 (2) 3 (3) 4 (4) 5

Short answer

4

Step-by-step solution

Understand Hexyne

Hexyne is an alkyne with the molecular formula \(\text{C}_6\text{H}_{10}\). The prefix 'hex-' indicates that it has six carbon atoms, and the suffix '-yne' indicates the presence of a triple bond.

Identify the Structure

A hexyne molecule has a linear carbon chain where the triple bond can be located at different positions. However, the linearity of carbon atoms is determined by the presence of sp-hybridized carbons, which occur due to the triple bond.

Find the Linear Carbons

In a hexyne molecule, the two carbons involved in the triple bond are sp-hybridized and linear. Additionally, each of these sp-hybridized carbons is connected to another carbon in the chain, so the total number of linear carbon atoms are those involved directly in and adjacent to the triple bond.

Count the Linear Carbons

Thus, the hexyne molecule will have the carbons forming the triple bond plus the carbons directly connected linearly to this bond, resulting in a total of 4 linear carbon atoms.

Key concepts

Alkyne Chemistry

Alkynes are a type of hydrocarbon characterized by having at least one carbon-carbon triple bond. This triple bond consists of one sigma bond and two pi bonds. Alkynes have the general formula \(\text{C}_n\text{H}_{2n-2}\). The presence of the triple bond makes alkynes unsaturated hydrocarbons, which means they have fewer hydrogen atoms than alkanes and alkenes.

Alkynes are typically more reactive than alkanes but less reactive than alkenes. This increased reactivity is because the triple bond provides regions of high electron density that can be attacked by reagents during chemical reactions.

Examples of alkyne reactions include:

• Hydrogenation: Adding hydrogen (\text{H}_2) to convert the alkyne into an alkane or alkene.
• Halogenation: Adding halogens (such as \text{Br}_2 or \text{Cl}_2) across the triple bond.
• Hydrohalogenation: Adding hydrogen halides (such as \text{HCl} or \text{HBr}) to form haloalkenes or haloalkanes.

Understanding the chemistry of alkynes is crucial when studying their structure and reactivity.

sp-hybridization

Hybridization is a concept that explains the bonding and geometry of atoms within molecules. In sp-hybridization, one s orbital mixes with one p orbital to form two equivalent sp hybrid orbitals. This type of hybridization occurs in carbon atoms that form triple bonds.
The triple bond in alkynes consists of one sigma bond formed by the overlap of sp hybrid orbitals and two pi bonds formed by the side-by-side overlap of unhybridized p orbitals. As a result, sp-hybridized carbon atoms have a linear geometry with a bond angle of 180 degrees.
Key points about sp-hybridization:

• Each sp-hybridized atom has two sp hybrid orbitals and two unhybridized p orbitals.
• This hybridization provides a linear arrangement of the bonded atoms.
• sp-hybridized carbons are involved in the formation of triple bonds, as seen in alkynes like hexyne.

Being aware of sp-hybridization helps explain why certain carbon atoms in a molecule appear linear.

Linear Carbon Atoms

In the context of molecules like hexyne, some carbon atoms adopt a linear arrangement due to sp-hybridization. The alignment happens because the carbon atoms involved in a triple bond are sp-hybridized. This hybridization forces these carbon atoms and their immediate neighbors to align in a straight line.
To identify linear carbon atoms in hexyne, follow these steps:

• Locate the triple bond in the molecule.
• Identify the two carbon atoms directly involved in the triple bond; these are sp-hybridized and linear.
• Note that the carbon atoms adjacent to these sp-hybridized carbons are also part of the linear arrangement due to their bond angle.

Thus, in hexyne (where the triple bond can be anywhere along the carbon chain), you can count a total of 4 linear carbon atoms:

• 2 carbon atoms directly involved in the triple bond (sp-hybridized and linear)
• 2 carbon atoms directly connected to the sp-hybridized carbons, retaining the linear arrangement

Understanding this concept is crucial for tackling questions involving the structure and geometry of alkyne molecules.