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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]

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]

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. 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.

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.

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.