Sharp difference in the change in molar volumes and enthalpy of dissolution of 2D and 3D molecules in solvents illustrated by the Diels-Alder reaction

© 2020 Elsevier B.V. A sharp difference in the change in the molar volume during the transition from the solid phase to the solution for a number of 2D molecules of reagents compared with 3D molecules of the Diels-Alder reaction adducts was observed. The dissolution of 2D crystal molecules is accompanied by a significant increase in volume (10–15%) with a dissolution enthalpy close in magnitude to the fusion enthalpy. A similar transition for 3D crystal molecules is often accompanied by an unexpected decrease in volume and even negative enthalpy of dissolution in inert solvents. The similar change in these parameters is also considered for a number of 3D molecules: 1,3,5-triphenylbenzene, hexaphenylbenzene, 9,10-diphenylanthracene, congressane, and C-60 fullerene. This can be explained by the fact that the surface of large 3D molecules in a solution can be much more thoroughly surrounded by solvent molecules than in its own environment. These results indicate that the values of activation and reaction volumes and their ratio (ΔV≠S/ΔVr-n, S) may be weakly related to the mechanism of non-polar cycloaddition reactions

Diels–Alder Reaction as an Indicator of Internal and External Factors Influencing the Rate and Equilibrium: Kinetics, Thermochemistry, Catalysis, and High Pressure. A Review

Abstract: The Diels–Alder reaction (DAR), in addition to its enormous synthetic potential, is the most reliable testing ground for quantitative research of the influence of various internal and external factors on the rate and equilibrium. The influence of the energy of intermolecular orbital interaction and then the influence of the enthalpy of reaction have been considered. It has been demonstrated that the DAR rate can be described when both factors are considered jointly. Kinetic and thermochemical data for DAR in the presence of Lewis acids are discussed. New data on the DAR rate during grinding reagents in the solid phase generate many problems for further study. Finally, the analysis of extensive data on the high pressure effect on the DAR rate and equilibrium have allowed the conclusion that differences in activation volumes and reaction volumes are not related to the mechanism of the DAR

Study of all stages of the Diels–Alder reaction of cyclopentadiene with 2,3-dicyano-1,4-benzoquinone and monoadducts: Kinetics, thermochemistry, and high pressure effect

© 2020 Wiley Periodicals, Inc. The kinetic parameters and enthalpies of the Diels–Alder reactions between cyclopentadiene and 2,3-dicyano-1,4-benzoquinone leading to the formation of two different monoadducts and bisadduct were determined. The stability of adducts is compared. Monoadduct appears to be thermodynamically more stable than the bisadduct. Comparison with the other Diels–Alder reactions studied previously allows us to conclude that the heat effects upon formation of the considered Diels–Alder adducts are the lowest in comparison with all the studied dienophiles

Sharp difference in the rate of formation and stability of the Diels–Alder reaction adducts with 2,3-dicyano-1,4-benzoquinone and N-phenylimide-1,4-benzoquinone-2,3-dicarboxylic acid

This work reports new studies of the activity and Diels–Alder kinetics of a series of dienophiles: tetracyanoethylene (1), 2,3-dicyano-p-benzoquinone (10), and N-phenylimide-1,4-benzoquinone-2,3-dicarboxylic acid (11). Rate differences are interpreted in terms of the donor–acceptor properties of the reagents. The relative π-acceptor properties of the dienophiles are probed by measuring their interaction energies with a series π-donor solvents: benzene, toluene, o-xylene, and chlorobenzene. The normalized interaction energies of 1, 10, and 11 are found to be 100:64:28. Despite the increased energy of the donor–acceptor interaction, dienophile 10 is 255 times less active in the reaction with 9,10-dimethylanthracene than 11. It is suggested that this is due to the significantly lower energy of π-bond cleavage in bicyclic dienophile 11, compared with monocyclic 10

Diels-Alder reaction rate in the solid state and the evidence of the location of molecular complexes between the reagents on the reaction pathway

The rate of reactions in the solid phase with uniform grinding of crystals of dienes, anthracene, and 9,10-dimethylanthracene, with dienophiles, tetracyanoethylene, N-phenylmaleimide, and 4-phenyl-1,2,4-triazoline-3,5-dione, has been studied. It was shown that, despite the high difference in the reaction rates in solution, the rates of these reactions in the solid phase are much closer. For anthracene-tetracyanoethylene and 9,10-dimethylanthracene-tetracyanoethylene pairs, it was concluded that their intermolecular complexes are on the reaction pathway

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta