1,721,050 research outputs found
Weak hydrogen bonds in adducts between freons: The rotational study of CH2F2–CH2ClF
No full textThe rotational spectra of 2 isotopologues of the molecular adduct CH2F2–CH2ClF show that the two
subunits are held together through two weak C–H F–C and one C–H Cl–C linkages, rather than
through three weak C–H F–C connections. This suggests the weak Cl H interaction to be observed
preferentially to a weak F H one. Structural information on these weak hydrogen bonds has been
obtained. The dissociation energy has been estimated from centrifugal distortion to be 5.3 kJ mol1
Rotational study of the bimolecule acetic acid-fluoroacetic acid
No full textThe rotational spectrum of the acetic acid-fluoroacetic acid bimolecule was measured by using a pulsed jet Fourier transform microwave spectrometer. One conformer, in which fluoroacetic acid is in trans form, has been observed. The rotational transitions are split into two component lines, due to the internal rotation of the methyl group of acetic acid. From these splittings, the corresponding V3 barrier has been determined. The dissociation energy of this complex has been estimated to 66 kJ/mol. An increase of the distance between the two monomers upon the OH → OD substitution (Ubbelohde effect) has been observed
Conformational equilibria and large-amplitude motions in dimers of carboxylic acids: rotational spectrum of acetic acid-difluoroacetic acid
No full textWe report the rotational spectra of two conformers of the acetic acid-difluoroacetic acid adduct (CH3COOH-CHF2COOH) and supply information on its internal dynamics. The two conformers differ from each other, depending on the trans or gauche orientation of the terminal -CHF2 group. Both conformers display splittings of the rotational transitions, due to the internal rotation of the methyl group of acetic acid. The corresponding barriers are determined to be V3(trans)=99.8(3) and V3(gauche)=90.5(9) cm(-1) (where V3 is the methyl rotation barrier height). The gauche form displays a further doubling of the rotational transitions, due to the tunneling motion of the -CHF2 group between its two equivalent conformations. The corresponding B2 barrier is estimated to be 108(2) cm(-1). The increase in the distance between the two monomers upon OH→OD deuteration (the Ubbelohde effect) is determined
The rotational spectrum of CF3Cl-Ar
No full textThe microwave spectrum of the van der Waals complex CF3Cl-Ar has been investigated by pulsed jet Fourier transform microwave spectroscopy. The observed spectra of the 35Cl and 37Cl isotopologues are typical of asymmetric tops, with rotational constants A, B, C = 3373.118(4), 988.2529(4), 879.5788(3) and 3286.66(4), 985.50(3), 871.359(8) MHz, respectively. The Ar atom is almost "L-shaped" with respect to the Cl-C bond, at a r0 distance of 3.824(2) Å from the center of mass (CM) of CF3Cl and with the angle Cl-CM-Ar = 81(2)°. The dissociation energy has been estimated to be 2.3 kJ mol-1
Rotational spectrum of the tetrafluoromethane-ethylene oxide
No full textThe rotational spectrum of one conformer of the CF4–ethylene oxide complex has been measured by using a pulsed jet Fourier-transform microwave spectrometer. The observed conformer is stabilized by a CF3⋯O halogen bond, with a distance rC⋯O of ∼3.341 Å. No experimental evidence of the internal rotation of CF4 with respect to ethylene oxide has been observed, but it is expected to be almost free (V3 ∼ 14 cm−1 from ab initio calculations)
The Barrier to Proton Transfer in the Dimer of Formic Acid: A Pure Rotational Study
Full text linkThe rotational spectra of three C-deuterated isotopologues of the dimer of formic acid have been measured, thanks to the small dipole moment induced by asymmetric H→D substitution(s). For the DCOOH–HCOOH species, the concerted double proton transfer of the two hydroxy hydrogen atoms takes place between two equivalent minima and generates a tunneling splitting of 331.2(6) MHz. This splitting can be reproduced by a 3D model with a barrier of 2559 cm−1 (30.6 kJ mol−1) as obtained from theoretical calculations
Conformational Equilibrium and Internal Dynamics of E-Anethole: A Rotational Study
No full textThe rotational spectra of the two conformers of E-anethole have been investigated using the free jet broadband millimeter-wave spectroscopic technique combined with theoretical calculations. Anti and syn conformers differ for the relative orientation of the propenyl and methoxy chains, with all heavy atoms coplanar to the benzene ring. Relative intensity measurements prove that the anti form is the global minimum, about 2.0(5) kJ mol-1 lower in energy with respect to the syn conformer, solving the contrasting results supplied by different theoretical methods. For both conformers, the barriers to internal rotation of the propenyl -CH3 group are low enough to generate fully resolved A-E splittings of the rotational transitions. The corresponding V3 barriers have been determined to be 7.080(5) and 6.978(4) kJ mol-1, respectively
Intermolecular Hydrogen Bonding in 2-Fluoropyridine-Water
No full textThe hydration of 2-fluoropyridine with one water molecule has been studied with a pulsed jet Fourier transform microwave technique. The rotational spectra of five isotopologues of the 1:1 complex have revealed the formation of a single most stable isomer. The observed cluster is characterized by an OH···N hydrogen bond and a CH···O weak hydrogen bond, where water is coplanar to the aromatic ring and acts in a double role of proton donor and proton acceptor
Conformational analysis of 1,4-butanediol: A microwave spectroscopy study
No full textThe rotational spectra of two conformers of 1,4-butanediol have been assigned by pulsed-jet Fouriertransform microwave spectroscopy. Both species display an intra-molecular OH O hydrogen bond. For the most stable conformer, the rotational spectra of four isotopologues (OH–OH, OD–OH, OH–OD and OD–OD) have been measured. The la-type transition of its two symmetric species, OH–OH and
OD–OD, are split into two evenly spaced component lines separated by 6.292(1) and 0.0137(5) MHz, respectively. These splittings are due to the concerted internal rotation of the two OH (or OD) alcoholic groups, which connects two equivalent minima. A partial rs structure has been obtained
Interactions between Freons: A Rotational Study of CH2F2-CH2Cl2
No full textThe rotational spectra of two
isotopologues of a 1:1 difluoromethane–
dichloromethane complex have
been investigated by pulsed-jet Fourier-
transform microwave spectroscopy.
The assigned (most stable) isomer has
Cs symmetry and it displays a network
of two CH···ClC and one CH···FC
weak hydrogen bonds, thus suggesting
that the former interactions are stronger.
The hyperfine structures owing to
35Cl (or 37Cl) quadrupolar effects have
been fully resolved, thus leading to an
accurate determination of the three diagonal
(cgg ; g=a, b, c) and the three
mixed quadrupole coupling constants
(cgg’; g, g’=a, b, c; g1⁄46 g’). Information
on the structural parameters of the hydrogen
bonds has been obtained. The
dissociation energy of the complex has
been estimated to be 7.6 kJmol1
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