= Solution
The rigid <naphthalene> core fixes the separation and directions of the two arm attachment points. In A they point from more separated regions of the core, so closure requires the flexible arms to span the core and adopt less favorable torsional arrangements. In B the closer, more convergent attachment geometry permits the UPy ends to meet with \b[less conformational <strain> and better preorganization].
Both rings gain similar local UPy hydrogen-bonding interactions, but A pays a larger deformation cost in its linkers and overall geometry. That can rationalize its higher calculated total <energy> and its greater tendency to open into intermolecular chains.
The quoted $50\,\mathrm{kJ\,mol^{-1}}$ is large compared with $RT\simeq2.48\,\mathrm{kJ\,mol^{-1}}$. Nevertheless a total-energy difference is not automatically a solution Gibbs free-energy difference: <solvent> and <entropy> contributions would be needed before converting it into an equilibrium population ratio.
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