A Quest for the Origin of Barrier to the Internal Rotation ofHydrogen Peroxide (H₂O₂) and Fluorine Peroxide (F₂O₂)

Abstract: 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-structuralmolecules, hydrogen peroxide, H₂O₂, and fluorine peroxide, F₂O₂ is performed. Thehydrogen peroxide is an important bio-oxidative compound generated in the body cells tofight infections and is an essential ingredient of our immune system. The fluorine peroxideis its analogue. We have tried to discern the interactions and energetic effects that entail thenonplanar skew conformation as the equilibrium shape of the molecules. The physicalprocess of the dynamics of internal rotation initiates the isomerization reaction and generatesinfinite number of conformations. The decomposed energy components faithfully display thephysical process of skewing and eclipsing as a function of torsional angles and hence aregood descriptors of the process of isomerization reaction of hydrogen peroxide (H₂O₂) anddioxygen difluoride (F₂O₂) associated with the dynamics of internal rotation. It is observedthat the one-center, two-center bonded and nonbonded interaction terms are sharply dividedin two groups. One group of interactions hinders the skewing and favours planar cis/transforms while the other group favours skewing and prefers the gauche conformation of themolecule. The principal energetic effect forcing the molecules into the nonplanar gaucheform is the variation “O–O’ bond energy with torsion in both the molecules. It isdemonstrated that the barrier is not a regional effect rather it is made by the conjoint actionof all one- and two-center bonding and nonbonding interactions comprising the entireframework of the molecule. The present study claims to reveal one amazing feature of non-bonded interactions. Computed results of nonbonding interactions demonstrate that thenature of interaction between two formally positively charged non-bonding H atoms (H^δ+ ----H^δ+ ) is not always repulsive and it is attractive as well; the nature of the non-bondinginteraction between formally negatively charged atom (‘O’) and formally positively charged(‘H’) atom, (O^δ−----H^δ+ ), is not always attractive but repulsive too; it is also demonstrated that the nature of the nonbonding interaction between strongly electronegative atoms, ( F^δ−-- --F^δ−), is not always repulsive and it may be attractive as well.