Ab initio study of chiral recognition in the propylene imine·hydrogen peroxide complex

A spectroscopic and ab initio study of the hydrogen peroxide–formic acid complex: hindering the internal motion of H2O2

Hydrogen peroxide imprints its chirality onto the H₂O₂–formic acid complex, which results in an asymmetric tunnelling potential.

Molecular recognition in 1 : 1 hydrogen-bonded complexes of oxirane and trans-2,3-dimethyloxirane with ethanol: a rotational spectroscopic and ab initio study

High resolution rotational spectroscopy complemented by ab initio calculations has been used to elucidate the diastereomeric interactions in 1 : 1 complexes of ethanol, a transient chiral alcohol, hydrogen-bonded to oxirane (achiral) or trans-2,3-dimethyloxirane (DMO, 2 stereocenters). Two conformers of oxirane[dot dot dot]ethanol and three conformers of DMO[dot dot dot]ethanol have been identified, and their structures as well as their stability ordering have been determined. This completes, together with previous results on the propylene oxide...ethanol complex (N. Borho and Y. Xu, Angew. Chem., 2007, 119, 2326-2329; Angew. Chem., Int. Ed., 2007, 46, 2276-2279.), the study of a set of model systems with zero, one, and two methyl functional groups at the hydrogen bond acceptor oxirane. The dependence of the observed rotational line intensities on pressure, nozzle temperature, and different carrier gases has been investigated for the case of DMO[dot dot dot]ethanol. This provides insight into the kinetical and thermodynamical influence on the formation of different conformers. Comparison of the subtle energy differences among the complexes and within each set of conformers allows for a detailed analysis of molecular recognition in this benchmark system.

High-resolution infrared spectroscopy and ab initio studies of the cyclopropane-carbon dioxide interaction

A jet-cooled high-resolution infrared spectrum of the cyclopropane-carbon dioxide complex was detected for the first time, using a rapid scan infrared spectrometer with an astigmatic multipass sample cell. The spectrum was recorded in the vicinity of the CO2 asymmetric stretching band (nu3) and exhibits a b-dipole selection rule. Altogether, over 200 lines were observed, assigned, and fitted to Watson's S-reduction Hamiltonian. Rotational and quartic distortion constants were obtained. The band origin was located at 2347.6263(2) cm(-1), redshifted by 1.5230(2) cm(-1) from the corresponding frequency of the CO2 monomer. The experimentally determined structure shows that CO2 lies next to a C-C bond edge and is perpendicular to the C3 ring, indicating that the interaction is characterized by the bonding between the carbon atom of CO2 and the pseudo-pi system of cyclopropane. The intermolecular distance between the carbon atom of CO2 and the center of mass of cyclopropane was determined to be 3.667(2) A. Complete ab initio geometry optimizations and harmonic frequency calculations were carried out at the level of second-order Moller-Plesset perturbation theory with four different basis sets: cc-pVDZ, 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ. The lowest-energy structure identified with the three larger basis sets is in accord with the experimental finding. In addition, a transition state was identified and the tunneling barrier height was computed.