The monohydrates of thenyl alcohol and thenyl mercaptan have been probed in a supersonic jet expansion using chirped-pulse and Fabry-Perot Fourier-transform microwave spectroscopy. The rotational ...spectra revealed a single isomer for each of the dimers. The thenyl alcohol hydrate is stabilized by an O-H O
w
hydrogen bond between the alcohol and water, with water acting as a proton acceptor and additionally engaging in an O
w
-H π interaction with the thenyl ring. Conversely, water behaves as a proton donor in the thenyl mercaptan hydrate, linking to the thiol group though an O
w
-H S hydrogen bond and secondary O
w
-H π interactions with the ring. In both dimers water retains internal mobility, as tunneling doublings in the spectrum confirm an internal rotation motion of water inside the cluster. The experimental results have been complemented with density-functional-theory molecular orbital calculations, binding energy decomposition and a topological analysis of the electronic density, providing a comparative description of the effects of hydrogen bonding of water to the alcohol and thiol groups in the dimers, relevant to understand hydrogen bonding to sulfur centers.
Water forms weak H-bonds with thenyl compounds, simultaneously retaining internal mobility in the dimer.
Weakly-bound intermolecular clusters constitute reductionist physical models for non-covalent interactions. Here we report the observation of the monomer, the dimer and the monohydrate of ...2-adamantanol, a secondary alcohol with a bulky ten-carbon aliphatic skeleton. The molecular species were generated in a supersonic jet expansion and characterized using broadband chirped-pulse microwave spectroscopy in the 2-8 GHz frequency region. Two different
-
O-H···O hydrogen-bonded isomers were observed for the dimer of 2-adamantanol, while a single isomer was observed for the monomer and the monohydrate. The experimental rotational parameters were compared with molecular orbital calculations using density functional theory (B3LYP-D3(BJ), B2PLYP-D3(BJ), CAM-B3LYP-D3(BJ), ωB97XD), additionally providing energetic and electron density characterization. The shallow potential energy surface makes the dimer an interesting case study to benchmark dispersion-corrected computational methods and conformational search procedures.
The crossing of two electronic potential surfaces (a conical intersection) should result in geometric phase effects even for molecular processes confined to the lower surface. However, recent quantum ...simulations of the hydrogen exchange reaction (H + H₂ rightwards arrow H₂ + H) have predicted a cancellation in such effects when product distributions are integrated over all scattering angles. We used a simple topological argument to extract reaction paths with different senses from a nuclear wave function that encircles a conical intersection. In the hydrogen-exchange reaction, these senses correspond to paths that cross one or two transition states. These two sets of paths scatter their products into different regions of space, which causes the cancellation in geometric phase effects. The analysis should generalize to other direct reactions.
The homodimers of transiently chiral molecules offer physical insight into the process of molecular recognition, the preference for homo or heterochiral aggregation and the nature of the non-covalent ...interactions stabilizing the adducts. We report the observation of the benzyl mercaptan dimer in the isolation conditions of a supersonic jet expansion, using broadband (chirped-pulse) microwave spectroscopy. A single homochiral isomer was observed for the dimer, stabilized by a cooperative sequence of S-H···S and S-H···π hydrogen bonds. The structural data, stabilization energies and energy decomposition describe these non-covalent interactions as weak and dispersion-controlled. A comparison is also provided with the benzyl alcohol dimer.
A multifaceted approach to hydrogen storage CHURCHARD, Andrew J; BANACH, Ewa; JARON, Tomasz ...
Physical chemistry chemical physics : PCCP,
01/2011, Letnik:
13, Številka:
38
Journal Article
Recenzirano
The widespread adoption of hydrogen as an energy carrier could bring significant benefits, but only if a number of currently intractable problems can be overcome. Not the least of these is the ...problem of storage, particularly when aimed at use onboard light-vehicles. The aim of this overview is to look in depth at a number of areas linked by the recently concluded HYDROGEN research network, representing an intentionally multi-faceted selection with the goal of advancing the field on a number of fronts simultaneously. For the general reader we provide a concise outline of the main approaches to storing hydrogen before moving on to detailed reviews of recent research in the solid chemical storage of hydrogen, and so provide an entry point for the interested reader on these diverse topics. The subjects covered include: the mechanisms of Ti catalysis in alanates; the kinetics of the borohydrides and the resulting limitations; novel transition metal catalysts for use with complex hydrides; less common borohydrides; protic-hydridic stores; metal ammines and novel approaches to nano-confined metal hydrides.
In the last decade, experiment and theory have expanded our vision of non‐covalent interactions (NCIs), shifting the focus from the conventional hydrogen bond to new bridging interactions involving a ...variety of weak donor/acceptor partners. Whereas most experimental data originate from condensed phases, the introduction of broadband (chirped‐pulse) microwave fast‐passage techniques has revolutionized the field of rotational spectroscopy, offering unexplored avenues for high‐resolution studies in the gas phase. We present an outlook of hot topics for rotational investigations on isolated intermolecular clusters generated in supersonic jet expansions. Rotational spectra offer very detailed structural data, easily discriminating the isomeric or isotopic composition and effectively cancelling any solvent, crystal, or matrix bias. The direct comparison with quantum mechanical predictions provides insight into the origin of the inter‐ and intramolecular interactions with much greater precision than any other spectroscopic technique, simultaneously serving as test‐bed for fine‐tuning of theoretical methods. We present recent examples of rotational investigations around three topics: oligomer formation, chiral recognition, and identification of halogen, chalcogen, pnicogen, or tetrel bonds. The selected examples illustrate the benefits of rotational spectroscopy for the structural and energetic assessment of inter‐/intramolecular interactions, which may help to move from fundamental research to applications in supramolecular chemistry and crystal engineering.
Rotating molecules: The role of rotational spectroscopy to investigate non‐covalent interactions by using mass‐ and interaction‐specific molecular aggregates generated and isolated in a supersonic jet expansion is reviewed and examples of recent investigations with halogens, chalcogens, and pnicogens as electrophile partners in R−A⋅⋅⋅B interactions are provided.
The hydrogen exchange reaction has a conical intersection and is therefore a prototype for studying geometric phase effects in reaction dynamics. We compute wave packets in hyperspherical coordinates ...for the reaction H
+
H
2 (
v
0=0,
j
0=0) → H
2
+
H, over the collision energy range
E
coll=0.75−2.02 eV, using the plane wave packet method. Geometric phase effects are not included. The wave packets visualise the quantum dynamics around the conical intersection and relate it to the centre-of-mass scattering angle. The wave packet fails to encircle the conical intersection, making slightly less than half a revolution. This provides a physical picture for why geometric phase effects in this reaction are expected to be reduced.
Two conformers of cyclohexanol and the cyclohexanol-water adduct have been characterized in a jet expansion using rotational spectroscopy. In the gas phase, cyclohexanol adopts an equatorial position ...for the hydroxyl group, with the two conformers differing in the orientation of the hydroxylic hydrogen, either gauche or trans with respect to the aliphatic hydrogen at C(1). Axial cyclohexanol was not detected in the jet. The transitions of the gauche conformer are split into two component lines due to the tunneling effect of the O-H internal rotation, which connects two equivalent gauche minima. The tunneling splitting in the vibrational ground state has been determined to be ΔE0+0- = 52(2) GHz. From this splitting, the inversion barriers connecting the two equivalent gauche conformers have been determined using a flexible model to be B2 = 377 cm-1. A single isomer is detected for the cyclohexanol-water dimer, in which the water molecule acts as a proton donor to the equatorial gauche ring. The presence of torsional tunneling in the adduct suggests a concerted large-amplitude-motion in which the internal rotation in the ring is accompanied by a torsion of the water molecule, to produce an equivalent enantiomer. The torsional tunneling in the adduct is reduced to ΔE0+0- = 32.7(4) GHz and the potential barrier in the complex increases to B2 = 494 cm-1.
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