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When hydrogen is completely replaced by fluorine, arenes become prone to forming a lone pair⋯π–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. An accurate analysis of the experimental data, including internal dynamics effects, endorsed by quantum chemical calculations, both with topological analysis and energy decomposition method, extended to the hydrogenated arenes and their water complexes, proved the ability of ammonia to create a stronger and more flexible lone pair⋯π–hole interaction than water. Interestingly, the higher binding energies of the ammonia lone pair⋯π–hole interactions correspond to larger intermolecular distances. [ABSTRACT FROM AUTHOR]

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–H…Cl–C and one C–H…F–C weak hydrogen bonds, combined with a Cl…F 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. Information on the rs positions of the two Cl atoms and on the structural parameters of the hydrogen bonds has been obtained. The dissociation energy of the complex has been estimated as 5.9 kJ mol−1. [ABSTRACT FROM AUTHOR]

The microwave spectra of hydroquinone and of its O–D mono- and di-deuterated species have been investigated in the frequency range 8–40 GHz. Only the cis rotamer, which possesses a permanent dipole moment, has been observed. For this conformer the rotational and quartic centrifugal distortion constants have been obtained and the dipole moment has been measured. No doubling due to internal rotation between the two equivalent minima of the hydroxyl groups has been resolved. [ABSTRACT FROM AUTHOR]

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. Each rotational transition is split into five component lines due to the internal rotations of two nonequivalent acetone methyl groups. The V3 barriers to internal rotation of the two CH3 tops of acetone were determined to be 252(4) and 220(1) cm−1, which are noticeably lower than the value for the monomer (266 cm−1). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We measured the molecular beam Fourier transform microwave spectra of six isotopologues of the 1 : 1 adduct of CH3CHClF with water. Water prefers to form an O–HF rather than an O–HCl hydrogen bond. This is just the contrary of what was observed in the chlorofluoromethane–water adduct, where an O–HCl 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–HF bridge to the fluorine atom, with r(FHw) = 2.14 Å, and with two C–HO contacts to the alkyl hydrogens with r(C1–H1Ow) = 2.75 Å and r(C2–H2Ow) = 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. [ABSTRACT FROM AUTHOR]

We observed the rotational spectrum of the 1 : 1 molecular adduct between 2-phenylethylamine and water (normal and H218O 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 gaucheconformation 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 Å) from the closest methylenic and aromatic hydrogen atoms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The rotational spectra of five vibrational states of pyridine have been assigned and measured by millimeter wave absorption spectroscopy in a supersonic expansion. The intensities of the lines of the vibrational satellites with respect to the ground state after the supersonic expansion depend on the kind of carrier gas, backing pressure, pyridine concentration, and symmetry of the rotational and vibrational states. Several rotational transitions of the vibrational satellites have also been measured in a conventional cell to complete the spectral assignment. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]