Understanding Saturated and Unsaturated Carbon Compounds

Let's analyze the given statements about carbon compounds to determine which ones are correct.

We are asked to identify the correct statement(s) regarding saturated and unsaturated carbon compounds and their reactivity.

Here are the statements:

1. Carbon compounds linked by only single bond are called saturated compounds.
2. Carbon compounds having double or triple bonds are called unsaturated compounds.
3. Saturated carbon compounds are more reactive than unsaturated carbon compounds.

Analysis of Statement I: Saturated Carbon Compounds

Statement I says: "Carbon compounds linked by only single bond are called saturated compounds."

Carbon atoms can form strong covalent bonds with other carbon atoms and with other elements like hydrogen. When all the valencies of carbon atoms are satisfied by single bonds, the compound is said to be saturated.

Example: Alkanes like ethane ($\text{C}_2\text{H}_6$) or propane ($\text{C}_3\text{H}_8$). In these compounds, all carbon-carbon and carbon-hydrogen bonds are single bonds.

Therefore, statement I is correct.

Analysis of Statement II: Unsaturated Carbon Compounds

Statement II says: "Carbon compounds having double or triple bonds are called unsaturated compounds."

When carbon compounds contain double bonds (C=C) or triple bonds (C$\equiv$C) between carbon atoms, they are called unsaturated compounds. These bonds represent 'unsaturation' because the carbon atoms could potentially bond with more atoms if the double or triple bonds were broken.

Examples:

• Alkenes like ethene ($\text{C}_2\text{H}_4$, contains a C=C double bond).
• Alkynes like ethyne ($\text{C}_2\text{H}_2$, contains a C$\equiv$C triple bond).

Therefore, statement II is correct.

Analysis of Statement III: Reactivity of Saturated vs. Unsaturated Compounds

Statement III says: "Saturated carbon compounds are more reactive than unsaturated carbon compounds."

The reactivity of hydrocarbons is often related to the types of bonds present. Saturated hydrocarbons (alkanes) primarily undergo substitution reactions, which generally require more energy to initiate because single bonds are relatively strong and stable.

Unsaturated hydrocarbons (alkenes and alkynes) contain double or triple bonds. The pi ($\pi$) part of these multiple bonds is less strong than the sigma ($\sigma$) part and is also more exposed. This makes unsaturated compounds prone to undergo addition reactions, where atoms are added across the double or triple bond, often under milder conditions compared to substitution reactions in alkanes.

Due to the presence of relatively weaker pi bonds, unsaturated compounds are generally more reactive than saturated compounds, especially towards addition reactions.

Therefore, statement III is incorrect.

Summary of Statements

Let's summarize our findings:

• Statement I: Correct
• Statement II: Correct
• Statement III: Incorrect

Based on the analysis, only statements I and II are correct.

We are looking for the option that states only I and II are correct.

Final Conclusion

Statements I and II are correct, while statement III is incorrect. The option that correctly identifies the correct statements is "Only I and II".

Revision Table: Carbon Compounds

Additional Information on Hydrocarbons and Reactivity

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon atoms. They are fundamental to organic chemistry.

• Saturated Hydrocarbons (Alkanes): Have the general formula $\text{C}_n\text{H}_{2n+2}$ for acyclic alkanes. They are relatively stable and undergo reactions like combustion, halogenation (substitution), and cracking.
• Unsaturated Hydrocarbons (Alkenes and Alkynes):
  • Alkenes have at least one carbon-carbon double bond (C=C) and the general formula $\text{C}_n\text{H}_{2n}$ for acyclic alkenes.
  • Alkynes have at least one carbon-carbon triple bond (C$\equiv$C) and the general formula $\text{C}_n\text{H}_{2n-2}$ for acyclic alkynes.
  These multiple bonds consist of one sigma ($\sigma$) bond and one or two pi ($\pi$) bonds. The pi bonds are weaker than sigma bonds and are easily attacked by electrophiles, leading to addition reactions where the multiple bond is converted into single bonds, and new atoms are added to the carbon chain. This makes alkenes and alkynes generally more reactive than alkanes, particularly in addition reactions like hydrogenation, halogenation, hydration, and hydrohalogenation.
• The reactivity order is generally Alkynes $\ge$ Alkenes > Alkanes, though specific reaction conditions and catalysts can influence this order.