Question

A/B Trans steroidal hydrogen in the 5th position

• A. Beta configuration
• B. Eclipsed conformation
• C. Alpha configuration
• D. Gauche conformation

Hint:

Remember: Trans A/B junction = H at C-5 in alpha position; Cis A/B junction = H at C-5 in beta position.

Answer 1

The Correct Option is C

- Steroids consist of four fused rings labeled A, B, C, and D. The configuration of hydrogen at the 5th carbon (C-5) determines the stereochemistry of the junction between rings A and B.
- If the hydrogen at the 5th position is in the alpha configuration (below the plane), it means the A/B ring junction is in trans configuration. This is typical for many biologically active steroids.
- In contrast, if the hydrogen is in the beta configuration (above the plane), the A/B junction is cis.
- Trans junctions generally offer more thermodynamic stability due to less steric strain compared to cis junctions.
- Hence, A/B trans steroidal configuration involves hydrogen at C-5 in the alpha position.