Question

The compound with molecular formula C\(_{20}\)H\(_{42}\) is

• A. Decane
• B. Dodecane
• C. Eicosane
• D. Hicosane

Hint:

Memorize the IUPAC root names for carbon chains, especially beyond ten carbons, as they are often tested.

• 11: Undecane
• 12: Dodecane
• 13: Tridecane
• 20: Eicosane
• 30: Triacontane

Answer 1

The Correct Option is C

Step 1: Identify the type of hydrocarbon.
The molecular formula is C\(_{20}\)H\(_{42}\). This fits the general formula for alkanes, C\(_n\)H\(_{2n+2}\). For n=20, 2n+2 = 2(20) + 2 = 40 + 2 = 42. So, the compound is a 20-carbon alkane.
Step 2: Recall the IUPAC nomenclature for alkanes.
The root name of an alkane indicates the number of carbon atoms in its longest chain. We need to identify the root name for a 20-carbon chain.

• (A) Decane: "Deca-" means 10. So, C\(_{10}\)H\(_{22}\).
• (B) Dodecane: "Do-" (2) + "deca-" (10) means 12. So, C\(_{12}\)H\(_{26}\).
• (C) Eicosane: "Eicosa-" is the Greek prefix for 20. So, C\(_{20}\)H\(_{42}\).
• (D) Hicosane: This is a common misspelling of Eicosane.

Step 3: Final Answer.
The correct name for the alkane with the molecular formula C\(_{20}\)H\(_{42}\) is Eicosane.