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: Understanding the Concept:
Acyclic alkanes follow the general mathematical formula $C_{n}H_{2n+2}$. The IUPAC nomenclature system utilizes specific Greek/Latin numerical prefixes to denote the exact number of carbon atoms in the main chain.
Step 2: Key Formula or Approach:
Verify it is an alkane, then match the carbon count ($n=20$) to the internationally recognized IUPAC prefix list for higher alkanes.
Step 3: Detailed Explanation:
1. Formula check: For $n=20$, the number of hydrogens is $H = 2(20) + 2 = 42$. This matches the given formula $C_{20}H_{42}$, confirming it is an alkane.

2. Nomenclature prefixes:
(A) Dec- is the prefix for 10 carbons. Decane is $C_{10}H_{22}$.
(B) Dodec- is the prefix for 12 carbons. Dodecane is $C_{12}H_{26}$.
(C) Eicos- is the universally accepted prefix for 20 carbons. Therefore, Eicosane is $C_{20}H_{42}$.
(D) Hicosane is a misspelling and not a standard IUPAC term; Eicosane is the correct Greek-derived root.
Step 4: Final Answer:
The compound containing 20 carbons is Eicosane.