Catalytic Activity of Complex-Oxide Perovskite-containing Compositions in Reactions of Oxidation of CO and Organic Compounds

The catalytic activity of composites constituted by a porous metallic or ceramic support, intermediate layers of oxide nature, and perovskite coatings, including those doped with silver, was studied in reactions of deep oxidation of CO and organic compounds of various classes. The relationship between the catalytic activity of a composite and its composition and nature of substances being oxidized was analyzed.     

Identifying Enantiomers in Mixtures of Chiral Molecules with Broadband Microwave Spectroscopy

Chirality‐sensitive broadband microwave spectroscopy was performed on mixtures of carvone enantiomers and conformers to distinguish enantiomers, measure enantiomeric excesses, and determine the absolute configurations of the enantiomers. This method uses microwave three‐wave mixing and is inherently well‐suited to the analysis of mixtures—a unique advantage over other techniques. In contrast to conventional microwave spectroscopy, the phase of the received signal is also exploited. This phase depends upon the signs of the molecules’ dipole‐moment components and is used to identify the excess enantiomer. The measured signal amplitude determines the size of the excess. The broadband capabilities of the spectrometer were used to simultaneously excite and measure two conformers of carvone, demonstrating the analysis of a sample with multiple chiral species. Employing quantum chemical calculations and the measured phases, the absolute configurations of the enantiomers are determined.     

IR-IR-UV hole-burning: conformation specific IR spectra in the face of UV spectral overlap

A new technique, IR-IR-UV hole-burning, is reported for obtaining conformation specific IR spectra when the electronic spectra are too closely overlapped to obtain clean spectra free from interference from other conformations via standard ion dip or fluorescence dip methods. The 4'-aminobenzo-15-crown-5 ether-(HDO) complex is used as an example, on which the method was applied to prove the presence of two conformations having overlapped electronic spectra and to assign IR transitions belonging to the same conformation.     

Entropy-driven population distributions in a prototypical molecule with two flexible side chains: O-(2-acetamidoethyl)-N-acetyltyramine

Resonant two-photon ionization (R2PI), resonant ion-dip infrared (RIDIR), and UV-UV hole-burning spectroscopies have been employed to obtain conformation-specific infrared and ultraviolet spectra under supersonic expansion conditions for O-(2-acetamidoethyl)-N-acetyltyramine (OANAT), a doubly substituted aromatic in which amide-containing alkyl and alkoxy side chains are located in para positions on a phenyl ring. For comparison, three single-chain analogs were also studied: (i) N-phenethyl-acetamide (NPEA), (ii) N-(p-methoxyphenethyl-acetamide) (NMPEA), and (iii) N-(2-phenoxyethyl)-acetamide (NPOEA). Six conformations of OANAT have been resolved, with S(0)-S(1) origins ranging from 34,536 to 35,711 cm(-1), denoted A-F, respectively. RIDIR spectra show that conformers A-C each possess an intense, broadened amide NH stretch fundamental shifted below 3400 cm(-1), indicative of the presence of an interchain H bond, while conformers D-F have both amide NH stretch fundamentals in the 3480-3495 cm(-1) region, consistent with independent-chain structures with two free NH groups. NPEA has a single conformer with S(0)-S(1) origin at 37,618 cm(-1). NMPEA has three conformers, two that dominate the R2P1 spectrum, with origin transitions between 35,580 and 35,632 cm(-1). Four conformations, one dominate and three minor, of NPOEA have been resolved with origins between 35,654 and 36,423 cm(-1). To aid the making of conformational assignments, the geometries of low-lying structures of all four molecules have been optimized and the associated harmonic vibrational frequencies calculated using density functional theory (DFT) and RIMP2 methods. The S(0)-S(1) adiabatic excitation energies have been calculated using the RICC2 method and vertical excitation energies using single-point time-dependent DFT. The sensitivity of the S(0)-S(1) energy separation in OANAT and NPOEA primarily arises from different orientations of the chain attached to the phenoxy group. Using the results of the single-chain analogs, tentative assignments have been made for the observed conformers of OANAT. The RIMP2 calculations predict that interchain H-bonded conformers of OANAT are 25-30 kJ/mol more stable than the extended-chain structures. However, the free energies of the interchain H-bonded and extended structures calculated at the preexpansion temperature (450 K) differ by less than 10 kJ/mol, and the number of extended structures far outweighs the number of H-bonded conformers. This entropy-driven effect explains the presence of the independent-chain conformers in the expansion, and cautions future studies that rely solely on relative energies of conformers in considering possible assignments.