What specific structural phenomenon prevents heavily substituted ortho-tetramethyl biphenyl systems — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Biphenyl systems consist of two phenyl rings joined by a single bond. When massive substituents are placed at all four ortho positions, severe steric hindrance occurs. To relieve this strain, the single bond rotates, locking the rings into mutually perpendicular planes. Perpendicular planes strictly forbid Geometrical Isomerism.