In a standard even-cumulene system possessing exactly two adjacent pi bonds (an allene framework), w — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

In an allene (even cumulene) system, the central $sp$ hybridized carbon forms two mutually perpendicular pi bonds using its two unhybridized p-orbitals. Consequently, the groups attached to the terminal $sp^2$ hybridized carbons are geometrically locked in mutually perpendicular planes. The dihedral angle spanning between these orthogonal terminal planes is $90^\circ$.