Accurate structure and torsional barrier heights of hydrogen peroxide

Chiral discrimination by vibrational spectroscopy utilizing local modes

Chiral discrimination of homochiral and heterochiral H-bonded complexes is a challenge for both experimentalists and computational chemists. It is demonstrated that a two-pronged approach based on far-infrared vibrational spectroscopy and the calculation of local mode frequencies facilitates the chiral discrimination of H-bonded dimers. The local H-bond stretching frequencies identify the strongest H-bonds and by this the dominating chiral diastereomer. This is shown in the case of peroxide, trioxide, hydrazine, glycidol, and butan-2-ol dimers as well as propylene oxide···glycidol complexes investigated with the help of second-order Møller-Plesset perturbation, coupled cluster, and density functional theory calculations where, in the latter case, the ωB97X-D functional was used for an improved description of H-bonding. In some cases, additional intermolecular interactions overrule the important role of H-bonding, which is found by calculating chirodiastaltic energies.

An intrinsic reaction coordinate calculation of the torsion-internal rotation potential of hydrogen peroxide and its isotopomers

Intrinsic reaction coordinate (IRC) calculations of the internal rotation (torsional) potentials for H(2)O(2) and its isotopomers HDO(2) and D(2)O(2) were carried out at the CCSD(T)/CBS//aug-cc-pVDZ level. Two extrapolation methods were used to obtain energies in the complete basis set (CBS) limit. The full IRC potential was constructed from scans from the C(2v) (cis) and C(2h) (trans) transition states to the equilibrium C(2) (gauche) structure. The IRC potential for H(2)O(2) was fit to a five-term Fourier function; coefficients were compared with values obtained from spectroscopic data. The twofold IRC torsional potentials were used to obtain torsional eigenvalues, which yielded values of the transitions between various ntau states. These results compare favorably with Raman and near-infrared data. Our calculations provide values of the cis and trans barriers of 2495 and 364 cm(-1), respectively, which are in good agreement with both previously calculated and experimentally derived values. It appears that coupling between torsional motion and other degrees of freedom is not significant in these molecules.