The following three alkenes are arranged in decreasing order of their bond rotational energy barriers. Consider their transition states to explain the difference in bond rotation energies.

• A. A. High bond rotation barrier due to unstable radicals in transition state.B. Lower bond rotation barrier due to resonance stabilized radicals in transition state.C. Lowest bond rotation barrier due to more resonance stabilized ions in transition state.
• B. A. High bond rotation barrier due to unstable ions in transition state.B. Lower bond rotation barrier due to resonance stabilized ions in transition state.C. Lowest bond rotation barrier due to more resonance stabilized ions in transition state.
• C. A. High bond rotation barrier due to resonance stabilized radicals in transition state.B. Lower bond rotation barrier due to less resonance stabilized radicals in transition state.C. Lowest bond rotation barrier due to no resonance stabilized ions in transition state.
• D. A. High bond rotation barrier due to small substituents on the double bond.B. Lower bond rotation barrier due to resonance stabilized radicals in transition state.C. Lowest bond rotation barrier due to large substituents on the double bond.

Answer: (A)