The strict restriction of free rotation around a carbon-carbon double bond, which essentially causes — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

A carbon-carbon double bond consists of one sigma bond and one pi bond. The pi bond is formed by the sideways (lateral) overlap of parallel unhybridized p-orbitals. Rotating one carbon atom by $90^\circ$ relative to the other destroys this overlap and breaks the pi bond, which requires substantial energy ($\sim 62$ kcal/mol). This energetic barrier rigidly freezes the spatial positions of the attached groups.