Question

How many rings present in cholesterol contain six carbon atoms?

• A. One
• B. Two
• C. Three
• D. Four

Hint:

Steroid Ring System (ABCD): Rings A, B, C = 6-Carbon rings (3 rings). Ring D = 5-Carbon ring (1 ring). Total = 4 fused rings (17 carbons in core).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The cyclopentanoperhydrophenanthrene (steroid) nucleus consists of three fused six-membered cyclohexane rings (A, B, C) and one five-membered cyclopentane ring (D).
Key Formula or Approach:
\[ \text{Steroid Nucleus: } \underbrace{\text{Ring A } (C_6) + \text{Ring B } (C_6) + \text{Ring C } (C_6)}_{\text{Three 6-Carbon Rings (Phenanthrene)}} + \underbrace{\text{Ring D } (C_5)}_{\text{One 5-Carbon Ring (Cyclopentane)}} \]

Step 2: Detailed Explanation:
In the molecular structure of Cholesterol:
- It possesses the characteristic tetracyclic fused hydrocarbon steroid core known as the cyclopentanoperhydrophenanthrene nucleus.
- Rings A, B, and C are six-membered cyclohexane rings containing six carbon atoms each (total of three 6-carbon rings).
- Ring D is a five-membered cyclopentane ring containing five carbon atoms.

Step 3: Final Answer:
Hence, Three rings in cholesterol contain six carbon atoms, matching option (C).