In order to understand the structure-property relationship, SPR, an energy-partitioning quest for the origin of the barrier to the internal rotation of two iso-structural molecules, hydrogen peroxide, H2O2, and fluorine peroxide, F2O2 is performed. The hydrogen peroxide is an important bio-oxidative compound generated in the body cells to fight infections and is an essential ingredient of our immune system. The fluorine peroxide is its analogue. We have tried to discern the interactions and energetic effects that entail the nonplanar skew conformation as the equilibrium shape of the molecules. The physical process of the dynamics of internal rotation initiates the isomerization reaction and generates infinite number of conformations. The decomposed energy components faithfully display the physical process of skewing and eclipsing as a function of torsional angles and hence are good descriptors of the process of isomerization reaction of hydrogen peroxide ( H2O2) and dioxygen difluoride (F2O2) associated with the dynamics of internal rotation. It is observed that the one-center, two-center bonded and nonbonded interaction terms are sharply divided in two groups. One group of interactions hinders the skewing and favours planar cis/trans forms while the other group favours skewing and prefers the gauche conformation of the molecule. The principal energetic effect forcing the molecules into the nonplanar gauche form is the variation "O-O' bond energy with torsion in both the molecules. It is demonstrated that the barrier is not a regional effect rather it is made by the conjoint action of all one- and two-center bonding and nonbonding interactions comprising the entire framework of the molecule. The present study claims to reveal one amazing feature of nonbonded interactions. Computed results of nonbonding interactions demonstrate that the nature of interaction between two formally positively charged non-bonding H atoms (H delta+---H delta+) is not always repulsive and it is attractive as well; the nature of the non-bonding interaction between formally negatively charged atom ('O') and formally positively charged ('H') atom, (O delta-----H delta+), is not always attractive but repulsive too; it is also demonstrated that the nature of the nonbonding interaction between strongly electronegative atoms, (F delta-----F delta-), is not always repulsive and it may be attractive as well.