Characterizing the lone pairπ-hole interaction in complexes of ammonia with perfluorinated arenes.

When hydrogen is completely replaced by fluorine, arenes become prone to forming a lone pairπ-hole non-covalent bond with ligands presenting electron rich regions. Such a species is ammonia, which confirms this behavior engaging its lone pair as the electron donor counterpart in the 1 : 1 adducts with hexafluorobenzene and pentafluoropyridine. In this work, the geometrical parameters of the interaction have been unambiguously identified through the detection, by means of Fourier transform microwave spectroscopy, of the rotational spectra of both normal species and their 15NH3 isotopologues.

Non covalent interactions stabilizing the chiral dimer of CHClF: a rotational study.

We report the rotational spectra of three isotopologues of the dimer of chlorofluoromethane, namely CH235ClF-CH235ClF, CH235ClF-CH237ClF and CH237ClF-CH235ClF. The assigned (most stable) conformer is chiral (C1 symmetry) and displays a network of two C-HCl-C and one C-HF-C weak hydrogen bonds, combined with a ClF halogen bond. The hyperfine structures due to the quadrupolar effects of the two non-equivalent 35Cl (or 37Cl) atoms have been fully resolved, leading to an accurate determination of two sets of diagonal and of some mixed quadrupole coupling constants.

Interactions between Ketones and Alcohols: Rotational Spectrum and Internal Dynamics of the Acetone-Ethanol Complex.

The rotational spectra of two isotopologues of the 1:1 complex formed between acetone and ethanol have been recorded and analyzed by using Fourier-transform microwave spectroscopy. One rotamer was detected, in which ethanol adopts the gauche form. The two subunits are linked by a conventional O-H⋅⋅⋅O and a weak C-H⋅⋅⋅O hydrogen bond, forming a six-membered ring.

Solving the Tautomeric Equilibrium of Purine through Analysis of the Complex Hyperfine Structure of the Four (14)N Nuclei.

The rotational spectra of two tautomers of purine have been measured by pulsed jet Fourier transform microwave spectroscopy coupled to a UV ultrafast vaporization system. The population ratio of the two main tautomers [N(7)H]/[N(9)H] is about 1/40 in the gas phase. It contrasts with the solid state where only the N(7)H species is present, or in solution where a mixture of both tautomers is observed.

Rotational Spectrum of Dichloromethane-Ne: Internal Dynamics and Cl Quadrupolar Hyperfine Effects.

The rotational spectra of three isotopologues, CH2(35)Cl2···(20)Ne, CH2(35)Cl(37)Cl···(20)Ne, and CH2(35)Cl2···(22)Ne, of the complex dichloromethane-neon have been assigned and measured by molecular beam Fourier transform microwave spectroscopy. The corresponding tunnelling splittings-due to the motion of Ne from above to below the ClCCl plane-have been determined as ΔE0+0- = 6.8900(5), 6.

The Cage Structure of Indan-CHF3 is Based on the Cooperative Effects of C-H⋅⋅⋅π and C-H⋅⋅⋅F Weak Hydrogen Bonds.

The structural and energetic features of the C-H⋅⋅⋅π interaction and the internal dynamics of the CHF3 group change drastically in going from benzene-CHF3 to indan-CHF3 , according to the analysis of the rotational spectrum of the latter complex generated in a supersonic expansion.

Interactions between carboxylic acids and aldehydes: a rotational study of HCOOH-CH2O.

The rotational spectrum of the 1:1 complex between formic acid and formaldehyde shows that the two units are linked together through a "classical" (OH···O) and a weak (CH···O) hydrogen bond. The molecular system appears quite rigid, and no effects of the internal motions have been observed in the spectrum.

Morphing the internal dynamics of acetylacetone by CH₃ → CF₃ substitutions. The rotational spectrum of trifluoroacetylacetone.

The rotational spectrum of trifluoroacetylacetone shows that the molecule exists in an enolic C(s) form and displays the features of internal rotations of the CH3 and CF3 groups, whose barriers to internal rotation were determined to be V3 = 379 and 30.8 cm(-1), respectively. Its internal dynamics appears to be intermediate between those of acetylacetone, where proton tunneling and low-barrier internal rotation of the two methyl groups make the spectrum quite complex, and hexafluoroacetylacetone, a perfectly "rigid" molecule on the time scale of microwave spectroscopy.

Pyridine-CF4: a molecule with a rotating cap.

The rotational spectrum of pyridine-CF4 has been investigated by molecular beam Fourier transform microwave spectroscopy in a supersonic expansion. The CF4 moiety is located as a cap over the pyridine nitrogen, and the two parts are freely rotating with respect to each other. For this reason, in a first approximation, in the m = 0 state only the pyridine ring is rotating along the a-axis, and the value of rotational constant A' is nearly the same of the constant A of isolated pyridine.

Keto-enol tautomerism and conformational landscape of 1,3-cyclohexanedione from its free jet millimeter-wave absorption spectrum.

The free jet millimeter-wave absorption spectrum of 1,3-cyclohexanedione has been investigated in the 59.6-74.4 GHz frequency range, and the rotational spectra of two conformational species, the chair-diketo and boat-diketo, and probably one excited vibrational state belonging to the chair-diketo form have been assigned.

Detection and characterization of impurities in commercial products with Fourier transform microwave spectroscopy.

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.

Rotational spectrum and internal dynamics of methylpyruvate.

The rotational spectra of five isotopologues (normal and all monosubstituted (13)C species) of methylpyruvate have been measured with the pulsed jet Fourier transform microwave technique. Rotational transitions are split into quintets due to the internal rotations of the two methyl groups. The corresponding barriers to internal rotation have been determined to be V(3)(H(3)C-O) = 4.

Proton transfer in homodimers of carboxylic acids: the rotational spectrum of the dimer of acrylic acid.

The dimer of acrylic acid can exist in two forms, depending on the entgegen or zusammen orientations of the two allyl groups. The latter one (zusammen) has a permanent value of the μ(b) dipole moment component, which allowed measuring its pulsed jet Fourier transform microwave (MW) spectrum. From the tunneling splitting, originating in the concerted proton transfer of the two carboxylic hydrogen atoms and measured for four isotopologues of such a bimolecule, we could determine the barrier and dynamics of the proton transfer.

Shapes and internal dynamics of the 1:1 adducts of ammonia with trans and gauche ethanol: a rotational study.

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.

On the weak O-H···halogen hydrogen bond: a rotational study of CH3CHClF···H2O.

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.

Conformational equilibria in diols: the rotational spectrum of chiral 1,3-butandiol.

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.

How trifluoroacetone interacts with water.

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.

Intertorsional interactions revealing absolute configurations: the V6 internal rotation heavy-top case of benzotrifluoride.

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.

The free jet microwave spectrum of 2-phenylethylamine-water.

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.

Hydrated complexes of atmospheric interest: rotational spectrum of diacetyl-water.

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.

Microwave spectrum of [1,1]-pyridine-Ne2.

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.

Methylsalicylate: a rotational spectroscopy study.

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.