Folding Free Energy Change
Exterior loops are stabilized by terminal mismatches, dangling ends, and coaxial stacks. The stacking is the optimal configuration of dangling ends, terminal mismatches, or coaxial stacks, noting that a nucleotide or helix end can participate in only one of these favorable interactions.
Folding Enthalpy Change
Similar to free energy change, exterior loop enthalpy changes are the sum of terminal mismatches, dangling ends, and coaxial stacks. The stacking is that of the lowest folding free energy change.