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ABSTRACT: The rotational signatures of methyl pyruvate as an impurity have been accidentally found and its rotational spectrum was assigned while recording the microwave spectrum of a 98% Sigma-Aldrich sample of methyl (S)-(-)-lactate with the pulsed jet Fourier transform microwave technique.
The Analyst 04/2013; 138(7):1959-61. · 4.23 Impact Factor
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ABSTRACT: 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.
Chemistry 08/2012; 18(40):12759-63. · 5.93 Impact Factor
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ABSTRACT: Dynamics and inertia: The rotation of the CF(3) top in α,α,α-trifluorotoluene becomes considerably hindered by a V(3) barrier in α,α,α-trifluoro-p-tolualdehyde. Situated in a local V(6) environment, the V(3) barrier is caused by the aldehyde group and communicated through the aromatic π system. Quite dramatically, the ground state inertial defect jumps from -1.271 to -89.961 uÅ(2) , thus reflecting the electronically induced rigidity.
Chemistry 02/2012; 18(9):2468-71. · 5.93 Impact Factor
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ABSTRACT: We measured the molecular beam Fourier transform microwave spectra of six isotopologues of the 1 : 1 adduct of CH(3)CHClF with water. Water prefers to form an O-H···F rather than an O-H···Cl hydrogen bond. This is just the contrary of what was observed in the chlorofluoromethane-water adduct, where an O-H···Cl link was formed (W. Caminati, S. Melandri, A. Maris and P. Ottaviani, Angew. Chem., Int. Ed., 2006, 45, 2438). The water molecule is linked with an O-H···F bridge to the fluorine atom, with r(F···H(w)) = 2.14 Å, and with two C-H···O contacts to the alkyl hydrogens with r(C(1)-H(1)···O(w)) = 2.75 Å and r(C(2)-H(2)···O(w)) = 2.84 Å, respectively. Besides the rotational constants, the quadrupole coupling constants of the chlorine atom have been determined. In addition, information on the internal dynamics has been obtained.
Physical Chemistry Chemical Physics 05/2011; 13(31):14092-6. · 3.57 Impact Factor
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ABSTRACT: The rotational spectra of five conformers of 1,3-butandiol have been measured by pulsed jet Fourier transform microwave spectroscopy. All of them are stabilized by an internal hydrogen bond and all of them have a GG' or a G'G arrangement of the two hydroxyl oxygens, which means that both oxygen atoms are on the same side with respect to the C1C2C3 plane. Apart from the spectroscopic constants, the relative abundances in the supersonic expansion are provided.
The Journal of Physical Chemistry A 03/2011; 115(34):9585-9. · 2.95 Impact Factor
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ABSTRACT: The rotational spectra of five isotopologues of the molecular adduct 1,1,1-trifluoroacetone-water have been assigned using pulsed-jet Fourier-transform microwave spectroscopy. All rotational transitions appear as doublets, due to the internal rotation of the methyl group. Analysis of the tunneling splittings allows one to determine accurately the height of the 3-fold barrier to internal rotation of the methyl group and its orientation, leading to V(3) = 3.29 kJ·mol(-1) and ∠(a,i) = 67.5°, respectively. The water molecule is linked to the keton molecule on the side of the methyl group through a O-H···O hydrogen bond and a C-H···O intermolecular contact, lying in the effective plane of symmetry of the complex.
The Journal of Physical Chemistry A 03/2011; 115(34):9493-7. · 2.95 Impact Factor
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ABSTRACT: a b s t r a c t The rotational spectra of five isotopologues of dimethyl sulfate have been assigned by pulsed-jet Fourier-transform microwave spectroscopy. The global minimum configuration has a C 2 symmetry, with the two methyl groups nearly trans with respect to the two sulfonic oxygen atoms. The internal rotations of the two methyl groups split each transition into several components line, allowing for the determination of accurate values of the V 3 barrier height to internal rotation and of the orientation of the methyl groups with respect to the principal axis system. The geometry of the molecular skeleton is fully determined.
Chemical Physics Letters 01/2011; · 2.34 Impact Factor
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ABSTRACT: We observed the rotational spectrum of the 1:1 molecular adduct between 2-phenylethylamine and water (normal and H(2)(18)O species) by free jet absorption microwave spectroscopy in the frequency region 60-78 GHz. The dominant spectrum belongs to the structure where the PEA moiety is in the most stable gauche conformation and the water molecule is hydrogen bound to the nitrogen lone pair. The orientation of the water molecule is such that the oxygen atom is almost equidistant (ca. 2.5 A) from the closest methylenic and aromatic hydrogen atoms.
Physical Chemistry Chemical Physics 09/2010; 12(35):10210-4. · 3.57 Impact Factor
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ABSTRACT: The microwave spectroscopic signatures of multiple torsional states of the CF(3) internal rotation in benzotrifluoride (alpha,alpha,alpha-trifluorotoluene) are reported. Individual rotational transitions are observed in a total of eight different torsional states, a quite challenging task for heavy tops even with Fourier transform microwave techniques. Accidental mixings of m = 0 and m = 3 torsional states as well as m = 1 and m = 2 torsional states, which can complicate the assignment of the spectra severely, are observed. These accidental mixings are probably systematic for molecules with heavy tops exhibiting an almost free internal rotation, and give an opportunity to determine the sign in the (1/2) V(6) (1+/-cos6tau) potential function hindering internal rotation and in consequence the orientation of the CF(3) top versus C(6)H(5) frame. A recently developed torsion-rotation program reproduces all line positions within an experimental accuracy of about 2.0 kHz. The V(6) barrier is determined to be 3.229949(32) cm(-1). The corresponding torsional spacings are determined with the seven-digit accuracy underlying the supersonic-jet Fourier transform microwave technique.
ChemPhysChem 08/2010; 11(12):2589-93. · 3.41 Impact Factor
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Chemistry 02/2010; 16(6):1761-4. · 5.93 Impact Factor
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ABSTRACT: The rotational spectrum of the molecular complex diacetyl-water has been measured by pulsed jet Fourier transform microwave (FTMW) spectroscopy. The water molecule acts as an electrofore and induces a dipole moment when combined with nonpolar diacetyl. Only one conformer has been observed, corresponding to the global minimum. Its shape is unambiguously established: the water moiety is linked asymmetrically to the organic molecule; it behaves as a proton donor to one of its oxygen atoms and interferes with the internal rotation of adjacent methyl group through a C-H...O interaction. Each rotational transition appears as a quintuplet, due to the internal rotation of the two methyl groups, which are nonequivalent in the adduct. From the analysis of the observed splittings, the V(3) barriers to the internal rotation of the two methyl groups have been determined to be 3.81(2) and 4.11(2) kJ/mol, respectively.
The Journal of Physical Chemistry A 12/2009; 113(52):14308-11. · 2.95 Impact Factor
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ABSTRACT: We investigated the rotational spectra of six isotopologues of pyridine−Ne2, formed by combinations of two isotopes of the nitrogen atom (14N and 15N) in pyridine with two isotopes of the rare gas atoms (20Ne and 22Ne), by using pulsed jet Fourier transform microwave spectroscopy. We detected the C2v symmetry conformer, denoted as [1,1], where the Ne atoms are located one on each side of the ring plane. The [2,0] species, with the two Ne atoms on the same side of the ring, was not observed. Two structural parameters, R and θ, that localize the rare gas atoms with respect to pyridine have been determined. The 14N nuclear quadrupole coupling constants have been obtained for the isotopologues containing this nucleus.
12/2009;
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ABSTRACT: We investigated the rotational spectra of six isotopologues of pyridine--Ne(2), formed by combinations of two isotopes of the nitrogen atom ((14)N and (15)N) in pyridine with two isotopes of the rare gas atoms ((20)Ne and (22)Ne), by using pulsed jet Fourier transform microwave spectroscopy. We detected the C(2v) symmetry conformer, denoted as [1,1], where the Ne atoms are located one on each side of the ring plane. The [2,0] species, with the two Ne atoms on the same side of the ring, was not observed. Two structural parameters, R and theta, that localize the rare gas atoms with respect to pyridine have been determined. The (14)N nuclear quadrupole coupling constants have been obtained for the isotopologues containing this nucleus.
The Journal of Physical Chemistry A 06/2009; 113(52):14227-30. · 2.95 Impact Factor
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Angewandte Chemie International Edition 01/2009; 48(6):1102-5. · 13.45 Impact Factor
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ABSTRACT: We report the free-jet rotational spectra of methylsalicylate, a molecule with a possible tautomeric and conformational equilibrium. In the ground electronic state, the molecule adopts a form stabilized by an intramolecular hydrogen bond between the phenolic hydrogen and the carbonylic oxygen, and this structure is characterized as the lowest-energy form by quantum chemical calculations. All rotational transitions are split because of the internal rotation of the methyl group, and the value of the barrier for this motion was determined to be V(3) = 5.38 kJ mol(-1).
The Journal of Physical Chemistry A 10/2007; 111(37):9076-9. · 2.95 Impact Factor
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ABSTRACT: The rotational spectra of normal and O-d species of the two most stable conformers of chiral 1-phenyl-1-propanol, obtained by free jet millimetre-wave absorption spectroscopy reveal that both conformers are stabilized by a O-H[dot dot dot]pi interaction, and have the Calpha-Cbeta-bond oriented nearly perpendicular to the plane of the benzene ring. The methyl group is trans with respect to the phenyl group for the most stable conformer (T), while it is gauche with respect to the phenyl group and entgegen with respect to the hydroxyl group for the second most stable conformer (GE). The energy difference (E(GE)-E(T)) was estimated to be 50(50) cm(-1) from relative intensity measurements.
Physical Chemistry Chemical Physics 09/2007; 9(32):4460-4. · 3.57 Impact Factor
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ABSTRACT: 4-Hydroxypyrimidine (4HP) has two conformational forms (the hydroxyl hydrogen cis or trans with respect to the adjacent nitrogen), which are in tautomeric equilibrium with two ketonic forms, 4-pyrimidinone (4PO) and 6-pyrimidinone (6PO). We have investigated the free jet absorption millimeterwave spectrum of this system, assigning the rotational spectra of 4HPcis and 4PO; the latter species is more stable by 2.0(9) kJ/mol. No lines corresponding to the trans isomer of 4-hydroxypyridine and to 6PO have been observed.
Journal of the American Chemical Society 06/2007; 129(19):6287-90. · 9.91 Impact Factor
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ABSTRACT: The rotational spectra of the main isotopomer, of the (29)Si and of all (13)C isotopologues of axial and equatorial forms of 1-fluoro-silacyclohexane have been measured by conventional (only main species) and molecular beam Fourier transform microwave spectroscopy. r(0) and partial r(s) structures are given separately for the two forms. The main structural differences are discussed. From dipole moments and relative intensity measurements, a slight preference (E(Eq) - E(Ax) = 42 +/- 24 cm(-1)) for the axial conformer was found. The rotational spectra of some, the most intense, vibrational satellites have also been measured. They belong to the ring-puckering motions.
The Journal of Physical Chemistry A 09/2006; 110(33):9995-9. · 2.95 Impact Factor
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ABSTRACT: The structural differences and the relative energies for the axial and equatorial forms of 1-methyl-1-silacyclohexane have been obtained from the rotational spectra of the normal, 29Si, and all 13C isotopologues of the axial and equatorial forms, observed by molecular beam Fourier transform microwave spectroscopy. The two species appear to have the same energy, within uncertainty limits, ΔE = 0.0 ± 0.2 kcal/mol. Structural parameters (r0 and rs) are given for the two forms. The main structural differences are discussed. Potential barriers for the methyl group internal rotations (V3) have been determined for both conformers to be 1.26(1) and 1.48(2) kcal/mol for the axial and equatorial species, respectively.
06/2006;
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ABSTRACT: The rotational spectrum of 1-benzofuran has been investigated by three different rotational spectroscopy techniques: (i) millimeterwave absorption free jet spectroscopy, useful for a fast assignment of the spectrum; (ii) molecular beam Fourier transform microwave spectroscopy, sensitive to detect less abundant isotopic species in natural abundance; (iii) waveguide conventional microwave spectroscopy, useful for the study of intramolecular dynamics, through the rotational spectra of the vibrational satellites of low energy modes. Besides the rotational spectrum of the ground state of the normal species, the spectra of 9 singly substituted 13C and 18O isotopomers in natural abundance, and of 6 vibrational satellites, have been measured. Precise structural parameters for the molecule, as well as information on the potential energy surface of the low energy vibrations, have been obtained. The dipole moment components have been determined to be micro(a)= 0.216 (2) and micro(b)= 0.720 (3) D, respectively.
Physical Chemistry Chemical Physics 10/2005; 7(18):3317-22. · 3.57 Impact Factor
