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Castel Guelfo di Bologna, Italy

Alonso J.L.,University of Valladolid | Vaquero V.,University of Valladolid | Pena I.,University of Valladolid | Lopez J.C.,University of Valladolid | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2013

Give me five! All five tautomers and conformers of cytosine were characterized in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy. The spectra were assigned unambiguously on the basis of the hyperfine structure due to the three 14N nuclei (see picture; N blue, O red). The relative energies of the identified species were estimated from the relative intensities of the spectra. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Melandri S.,amician Delluniversita | Evangelisti L.,amician Delluniversita | Maris A.,amician Delluniversita | Caminati W.,amician Delluniversita | And 4 more authors.
Journal of the American Chemical Society | Year: 2010

Millimeter wave free jet absorption and core level photoemission spectroscopies give complementary and precise information on the conformational/tautomeric equilibrium of 2-mercaptopyridine. © 2010 American Chemical Society. Source

Evangelisti L.,University of the Basque Country | Evangelisti L.,amician Delluniversita | Ecija P.,University of the Basque Country | Cocinero E.J.,University of the Basque Country | And 4 more authors.
Journal of Physical Chemistry Letters | Year: 2012

Tunneling effects have been measured in the pulsed jet Fourier transform microwave spectra of two isotopologues of the benzoic acid-formic acid bimolecule. The tunneling splittings are originated by the concerted proton transfer of the two carboxylic hydrogens. From the values of these splittings for the OH-OH and OD-OD species, it has been possible to model/size the barrier to the concerted double proton transfer. © 2012 American Chemical Society. Source

Lesarri A.,University of Valladolid | Cocinero E.J.,University of the Basque Country | Evangelisti L.,amician Delluniversita | Suenram R.D.,University of Virginia | And 2 more authors.
Chemistry - A European Journal | Year: 2010

The conformational landscape of the alkaloid anabasine (neonicotine) has been investigated by using rotational spectroscopy and ab initio calculations. The results allow a detailed comparison of the structural properties of the prototype piperidinic and pyrrolidinic nicotinoids (anabasine vs. nicotine). Anabasine adopts two most stable conformations in isolation conditions, for which we determined accurate rotational and nuclear quadrupole coupling parameters. The preferred conformations are characterized by an equatorial pyridine moiety and additional N-H equatorial stereochemistry at the piperidine ring (eq-eq; eq= equatorial). The two rings of anabasine are close to a bisecting arrangement, with the observed conformations differing by an approximately 1808 rotation of the pyridine subunit, denoted either syn or anti. The preference of anabasine for the eq-eq-syn conformation has been established by relative intensity measurements (syn/anti ∼ 5(2)). The conformational preferences of free anabasine are directed by a weak N···H C hydrogen bond interaction between the nitrogen lone pair at piperidine and the closest C-H bond in pyridine, with N···H distances ranging from 2.686 (syn) to 2.667 Å (anti). Supporting ab initio calculations by using MP2 and the recent M05-2X density functional are provided, evaluating the predictive performance of both methods. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Giuliano B.M.,amician Delluniversita | Favero L.B.,CNR Institute of Nanostructured Materials | Maris A.,amician Delluniversita | Caminati W.,amician Delluniversita
Chemistry - A European Journal | Year: 2012

Two 1:1 adducts of ammonia with ethanol have been characterized by using pulsed-jet FT microwave spectroscopy. They are formed with two different (trans and gauche), stable conformers of ethanol. Several internal-dynamics effects are reflected in the features of the rotational spectra. The trans complex shows the tunneling effects owing to internal rotation of both ammonia and the methyl group. The rotational transitions of the gauche species exhibit a small splitting that is related to tunneling through the potential-energy barrier between the two equivalent minima. A complex situation: Two different conformers of the ethanol-NH3 complex have been characterized by Fourier transform microwave spectroscopy. NH3 is linked to the gauche or trans forms of ethanol through an O-H⋯N hydrogen bond. The effects of three large amplitude motions (internal rotation of the CH3 group, almost-free rotation of the NH3 moiety, and tunneling between the two equivalent gauche forms) were observed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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