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Firkala T.,Budapest University of Technology and Economics | Talas E.,Hungarian Academy of Sciences | Kristyan S.,Hungarian Academy of Sciences | Szoll'si G.,MTA SZTE Stereochemistry Research Group | And 3 more authors.
Journal of Raman Spectroscopy | Year: 2015

The strength and geometry of adsorption of substituted propenoic acids on silver surface were studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. Based on their SERS behavior, two classes of phenylpropenoic acids studied were distinguished. The first class of propenoic acids (atropic acid, (E)-2,3-diphenylpropenoic acid, (E)-2-(2-methoxyphenyl)-3-phenylpropenoic acid, (E)-2,3-di-(4-methoxyphenyl)phenylpropenoic acid and (E)-2-(2-methoxyphenyl)-3-(4-fluorophenyl)propenoic acid) has shown strong charge transfer (CT) effect. We suggest bidentate carboxyl bonded species based on the SERS enhanced bands of νCOO- around 1394 cm-1 and νC-C of the -C-COO- moiety at 951 cm-1. In these series the plane of the α-phenyl group (γCH out-of-plane vibrations at 850-700 cm-1) is almost parallel to the silver surface, while the β-phenyl group is in tilted position depending on the type and the position of substituent(s) showing strong SERS enhanced bands of νCC + βCH (in-plane mode) at 1075 cm-1, νCC (ring breathing mode, in-plane) at 1000 cm-1 and γCCC (out-of-plane mode) around 401 cm-1. The other class of propenoic acids (cinnamic acid, (E)-2-phenyl-3-(4-methoxyphenyl)propenoic acid) has shown weak electromagnetic (EM) enhancement (CC bands is enhanced in cinnamic acid). In this case no significant carboxyl enhancement was observed, so we suggest that adsorbed species lie parallel to the surface. The two types of adsorption can be related to the dissociation ability of the carboxylic group. In the first case the carboxylic H dissociates, while in the second case it does not, as indicated also by the characteristic νCO band at 1686 cm-1 in the FT-Raman spectra of methanolic solutions. Copyright © 2015 John Wiley & Sons, Ltd. Source

Chen K.-Y.,University of Groningen | Wezenberg S.J.,University of Groningen | Carroll G.T.,University of Groningen | London G.,University of Groningen | And 4 more authors.
Journal of Organic Chemistry | Year: 2014

The design, synthesis, and dynamic behavior of a series of novel tetrapodal molecular switches and motors containing common functional groups for attachment to various inorganic and organic surfaces are presented. Using a Diels-Alder reaction, an anthracene unit with four functionalized alkyl substituents ("legs") was coupled to maleimide-functionalized molecular switches or motors under ambient conditions. Terminal functional groups at the "legs" include thioacetates and azides, making these switches and motors ideal candidates for attachment to metallic or alkyne-functionalized surfaces. UV/vis absorption spectroscopy shows that the molecular switches and motors retain their ability to undergo reversible photoinduced and/or thermally induced structural changes after attachment to the tetrapodal anthracene. © 2014 American Chemical Society. Source

Makra Z.,University of Szeged | Szollosi G.,MTA SZTE Stereochemistry Research Group
Catalysis Communications | Year: 2014

The effect of the solvent, modifier structure and concentration on the enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid over Pd/Al 2O3 modified by cinchona alkaloids was influenced by the addition of achiral amines to the reaction slurry. The solvent dependence in the presence of achiral amines showed that additives are involved in the rate determinant step of the reaction, whereas the effect of the dilution pointed to the presence of the acid dimers in the intermediate responsible for enantioselection. The dependence of the enantioselectivity on the cinchonidine concentration in the presence of amines and results obtained using cinchona derivatives and mixtures thereof were in line with our earlier assumptions related to the participation of the amine additive in the formation of the surface intermediate. Based on these and previously published results possible structures of this intermediate are suggested. © 2013 Elsevier B.V. Source

Cao J.,ETH Zurich | London G.,ETH Zurich | London G.,MTA SZTE Stereochemistry Research Group | Dumele O.,ETH Zurich | And 6 more authors.
Journal of the American Chemical Society | Year: 2015

Three series of stable, neutral, π-extended bispentalene derivatives, with two pentalenes fused to a central benzene or naphthalene moiety, have been prepared through a modified double carbopalladation cascade reaction. While these chromophores feature skeletons with [4n+2] π-electron perimeters, the two 8 π-electron pentalene subunits strongly influence bonding and spectral properties. 1H NMR spectra showed large upfield shifts of the protons in the pentalene moieties, comparable to antiaromatic monobenzopentalenes. Further investigations on magnetic ring currents through NICS-XY-scans suggest a global paratropic current and a local diatropic current at the central benzene ring in two of the series, while the third series, with a central naphthalene ring, showed more localized ring currents, with stronger paratropic ring currents on the pentalene moieties. X-ray diffraction analyses revealed planar bispentalene cores with large double- and single-bond alternation in the pentalene units, characteristic for antiaromaticity, and small alternation in the central aromatic rings. In agreement with TD-DFT calculations, both optical and electrochemical data showed much smaller HOMO-LUMO energy gaps compared to other neutral, acene-like hydrocarbons with the same number of fused rings. Both experimental and computational results suggest that the molecular properties of the presented bispentalenes are dominated by the antiaromatic pentalene-subunits despite the [4n+2] π-electron perimeter of the skeletons. (Chemical Equation Presented). © 2015 American Chemical Society. Source

Szollosi G.,MTA SZTE Stereochemistry Research Group | Fekete M.,University of Szeged | Gurka A.A.,University of Szeged | Bartok M.,MTA SZTE Stereochemistry Research Group | Bartok M.,University of Szeged
Catalysis Letters | Year: 2014

We report new results on the aldol reactions between aldehydes of three different types (aromatic, aliphatic and cycloaliphatic) and acetone/cycloalkanones as reaction partners, driven by organic-inorganic hybrid catalyst Pro/λ-Al2O3. In contrast to the homogeneous liquidphase reaction, over Pro/λ-Al2O 3reversal of the enantioselection in up to 20-40 % ee depending on the structure of the aldehyde was observed in reactions of acetone. Reversal of the ee in the presence of c-Al2O3cannot be generalized, as it has only been observed for acetone among the ketones studied by us. It was proven using methods of a great variety such as ultrasonic irradiation, reuse measurements on used catalyst and the filtrate of the first reaction, measurements on the L-Pro-L-Pro(OH) dipeptide, studies using mixtures of L-Pro and D-Pro that the organic-inorganic hybrid catalyst Pro/λ-Al 2O3formed in situ is responsible for reversal of the ee. In the reactions of cycloalkanones there is presumably competition between the liquid-phase and the surface reaction over Pro/ c-Al2O 3with preference for the former. Based on these results a surface reaction pathway was proposed. Although, the ees obtained under heterogeneous catalytic conditions are low, further studies may lead to application of this unusual phenomenon for obtaining chiral heterogeneous catalysts suitable for the preparation of the desired enantiomer of a chiral compound using the same chiral source. © Springer Science+Business Media New York 2013. Source

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