1,721,222 research outputs found
The rotational spectra of conformers of biomolecules: tryptamine
No full textThe rotational spectra of two conformers of tryptamine have been assigned by free jet millimeter-wave
absorption spectroscopy. Both of them are stabilized by an intramolecular N–H p bridge, formed between
the amino group of the lateral chain in position 3 and the p system of the pyrrole unity. They correspond to
the two most stable conformers found by resonant ion-dip infrared and UV–UV hole burning spectroscopies
[J. R. Carney and T. S. Zwier, J. Phys. Chem, 2000, 104, 8677]
Modeling the internal rotation tunnelling in benzyl alcohol by ring fluorination: The rotational spectrum of 3,5-difluorobenzyl alcohol
No full textThe rotational spectra of the –OH and –OD isotopologues of 3,5-difluorobenzyl alcohol have been measured by pulsed jet Fourier transform microwave spectroscopy. The main structural evidence is that the OCα-C1C2 dihedral angle, approximately 20° is ca. 40° smaller than in benzyl alcohol. This difference is reflected in the features of the rotational spectrum: μc-type (instead of μb-) transitions are split into two evenly spaced component lines (by 14.367(1) × 2 MHz) showing that the CH2OH group undergoes a tunnelling motion which connects two equivalent minima above and below the aromatic ring. The barrier for the interconversion of the two mirror form has been estimated from the experimental tunnelling splitting to be 380 cm−1
Ring fluorination effects on molecular water clusters: the cases of 2-fluoropyridine, 3-fluoropyridine and penta-fluoropyridine. A rotational spectroscopy study.
No full textThe importance of organic fluorinated compounds in science and in everyday life is growing year after year.1 The effects of fluorination are related to the high electronegativity of this atom and its polarizability. In general the introduction of a fluorine atom is used in order to modulate physicochemical properties, like hydrophilicity and lipophilicity, of bio-organic molecules and functional materials.1,2 Additionally, structural changes can also be related to the electronic effect of the fluorine atom or to the molecule capability of creating new hydrogen bonds or non-covalent bonds, having fluorine as acceptor.
For this reason we investigate clusters where a molecule of water is used as a probe to reveal the changes on the electrostatic potential on the fluorinated compounds.
The experimental conditions are achieved in supersonic expansions using Molecular Beam Fourier Transform Microwave Spectroscopy technique (MBFTMW).3 The high resolution and sensitivity of rotational spectroscopy give direct access to the structural arrangement of the systems, allowing the measurement of bond lengths and angles. Moreover this gas phase technique allows unveiling subtle structural and dynamical effects usually related to changes in non-covalent interactions.
The series of clusters studied between different fluorinated pyridines and a molecule of water are: 2-fluoropyridine-water, 3-fluoropyridine-water and penta-fluoropyridine-water (see Figure 1) complexes. The results clearly show that the introduction of a single fluorine atom into a molecule already induces significant effects, but as the number of fluorine atoms increases, such as in the case of penta-fluoropyridine, the system starts to behave as a completely novel species.4 The perfluorination effect is clearly observable in the penta-fluoropyridine-water adduct where the water oxygen lone pairs point towards the aromatic ring.
Figure 1: the observed adducts of 2-fluoropyridine, 3-fluoropyridine and penta-fluoropyridine with a molecule of water
Internal motions of the rare gas atom in dimethyl ether-krypton
No full textThe free jet millimeter-wave absorption spectra of two isotopomers of the weakly bonded dimethyl ether-Kr complex have been assigned and measured. The Kr atom lies in the óV symmetry plane of dimethyl ether perpendicular to the COC plane, at a r0-distance of 3.67 Å from its center of mass (cm). The line connecting the krypton atom to cm forms an r0-angle of 70° with the O-cm line. The observed conformation is in agreement with the global minimum as found with a distributed polarizability model. Many rotational transitions are split into two component lines, due to the motion of Kr relative to dimethyl ether in the complex. The corresponding splitting has been used to determine the barrier to the internal motion. Information on the dissociation energy has been deduced from the centrifugal distortion effects
Atropisomerism in bisphenols: free jet absorption millimeter wave study of 2,2’-biphenol
No full textThe rotational spectrum of 2,20-biphenol has been investigated by millimeter wave absorption free jet spectroscopy. The two sides of the phenyl rings with attached the hydroxyl group form a dihedral angle of 112.78. Each hydroxyl group is nearly co-planar to the ring to which it belongs, and points towards the p system of the adjacent ring
Advancements in Microwave Spectroscopy
No full textAbout 10 years ago we published two chapters concerning microwave spectroscopy in the first Elsevier book on Frontiers in Molecular Spectroscopy. One of them was concerning the most interesting molecular systems investigated by rotational spectroscopy and the second one the most recent advancements in the related techniques.During the last years, new exciting experiments have been described; probably the most important is the chiral discrimination by double-quantum coherence phase inversion and the diffusion of the chirp techniques.The implementation of "broadband chirp excitation" spectrometers and further development of "single-tone excitation" Fourier transform microwave spectroscopy, most favorably combining with supersonic-jet expansion techniques that make use of various pulse sources, most notably laser ablation sources, allowed for an extensive collection of data.Many of the investigated molecular systems are aimed to solve chemical problems or related to the internal dynamics.A great effort has been devoted to the recording of spectra of species of astrochemical interest, and many new chemical compounds have been observed in the interstellar or circumstellar medium and also comets or planetary atmospheres.A number of interesting examples, achieved in the last 10 years, are compiled here
Isotopomeric Conformational Change in Anisole-Water
No full textThe deuteration of water produces a conformational change in the Anisole×××Water complex, as shown by the scheme. The value of the q angle decreases from 138 to 128°, while the secondary interaction O×××HMe is replaced by the O×××HPh one
Interactions between organic molecules and water. Rotational spectrum of the 1:1 oxetane-water complex
No full textThe 1:1 molecular complex between oxetane and water has been
investigated by using free-jet millimeter-wave spectroscopy. The rotational spectra of five isotopomers (with H2O, D2O, DOH, HOD and H218O) have been assigned. Partial r0 and rs structures
of the complex have been derived. The water moiety lies in the
plane of symmetry of oxetane, with the TMfree∫ hydrogen E with respect to the ring. The oxetane ring appears to be slightly nonplanar, with the Cb carbon tilted on the opposite side of the water unity. The three atoms involved in the hydrogen bond adopt a linear arrangement with an Oring¥¥¥H distance of about 1.86 ä, and the angle between the COC bisector and the Oring¥¥¥H
bond being ffi1068. Additionally, quantum-chemical calculations for the complex were performed and were found to be in agreement with the experimental results
Conformational preferences of molecules, biomolecules and molecular complexes: the importance of the hydrogen bond and other non-bonding interactions
No full textUnveiling the Conformations and van der Waals Interactions between Rare Gas and Bicyclic Aromatic: Rotational Spectroscopy of Benzofuran Complexes with Argon and Krypton
No full textBy integrating Fourier transform microwave spectroscopy with quantum chemical calculations, a detailed conformational and structural analysis of the benzofuran (BF) complexes with argon (BF–Ar) and krypton (BF–Kr) is conducted. The conformations of each complex are explored utilizing the Conformer-Rotamer Ensemble Sampling Tool method for conformational searches, with subsequent geometry optimizations using MP2, RI-SCS-MP2, and density functional theory methods. Experimental results corroborate that the most stable conformations for both complexes feature the rare gas (Rg) atom positioned above the BF ring. In particular, Ar and Kr atoms prefer to locate above the C5 atom, with the Rg···C5 line nearly perpendicular to the BF plane. The Ar and Kr atoms are located ≈3.491 and 3.580 Å from the center of mass of BF. The natural bond orbital analysis indicates that the second-order perturbation energy for the Rg···π interaction is about 3.1 and 3.0 kJ mol−1 in the BF–Ar and BF–Kr complexes, respectively. Symmetry-adapted perturbation theory energy decomposition analysis reveals that dispersion forces are predominant in these complexes. This study provides insights into the nature of van der Waals interactions between bicyclic heteroaromatics and Rg
- …
