Question #44457

The conformational landscapes of 1,2-difluoroethane (Molecule A) and $N$-methylacetamide (Molecule B) exhibit significant deviations from simple steric models. Consider the following statements regarding their structural and thermodynamic properties at 298 K:

I. The global energy minimum of A corresponds to a F-C-C-F dihedral angle $\theta \approx 60^\circ$, primarily stabilized by two antiperiplanar $\sigma_{C-H} \rightarrow \sigma^*_{C-F}$ hyperconjugative interactions. II. The global energy minimum of B corresponds to a C-C-N-C dihedral angle $\omega \approx 180^\circ$, dictated by $n_N \rightarrow \pi^*_{C=O}$ delocalization and minimization of steric strain. III. In highly polar solvents, the anti conformer of A becomes the global energy minimum because its zero dipole moment minimizes unfavorable solvent interactions. IV. The activation energy for rotation around the C-N bond in B is approximately $85 \text{ kJ/mol}$, which is significantly higher than the C-C rotational barrier in A.

Which of the following combinations of statements is correct?