Question

General formula of alkynes

• A. \(\text{C}_n\text{H}_{2n}\)
• B. \(\text{C}_n\text{H}_{n}\)
• C. \(\text{C}_n\text{H}_{2n+2}\)
• D. \(\text{C}_n\text{H}_{2n-2}\)

Answer 1

The Correct Option is D

To determine the general formula of alkynes, we need to understand their structure and properties.

1. Understanding Alkynes:
Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond ($\equiv$). The simplest alkyne is ethyne (acetylene), with the molecular formula $\text{C}_2\text{H}_2$. The general characteristics of alkynes include:
- They have a general molecular formula of $\text{C}_n\text{H}_{2n-2}$.
- Each carbon atom in an alkyne contributes to the hydrogen count based on its degree of unsaturation. A triple bond reduces the number of hydrogen atoms by 2 compared to the corresponding saturated hydrocarbon (alkane).

2. General Formula Derivation:
For an alkane with $n$ carbon atoms, the general formula is $\text{C}_n\text{H}_{2n+2}$. However, each triple bond introduces a degree of unsaturation that removes 2 hydrogen atoms. Since alkynes have at least one triple bond, the general formula for alkynes is:

$$ \text{C}_n\text{H}_{2n-2} $$

3. Verifying the Options:
Let us evaluate the given options:
1. $\text{C}_n\text{H}_{2n}$: This is the general formula for alkenes (hydrocarbons with double bonds).
2. $\text{C}_n\text{H}_n$: This does not match the structure of any common class of hydrocarbons.
3. $\text{C}_n\text{H}_{2n+2}$: This is the general formula for alkanes (saturated hydrocarbons).
4. $\text{C}_n\text{H}_{2n-2}$: This is the correct general formula for alkynes, as derived above.

Final Answer: $ {\text{C}_n\text{H}_{2n-2}} $