A New Golden Age for Donor-Acceptor Cyclopropanes Schneider, Tobias F.; Kaschel, Johannes; Werz, Daniel B.
Angewandte Chemie (International ed.),
May 26, 2014, Volume:
53, Issue:
22
Journal Article
Peer reviewed
Open access
The effective use of ring strain has been applied to considerable advantage for the construction of complex systems. The focus here is directed towards cyclopropanes as building blocks for organic ...synthesis. Although thermodynamics should take the side of synthetic chemists, only a specific substitution pattern at the cyclopropane ring allows for particularly mild, efficient, and selective transformations. The required decrease in the activation barrier is achieved by the combined effects of vicinal electron‐donating and electron‐accepting moieties. This Review highlights the appropriate tools for successfully employing donor–acceptor cyclopropanes in ring‐opening reactions, cycloadditions, and rearrangements.
Tug‐of‐war on cyclopropanes: Even though donor–acceptor‐substituted cyclopropanes were already investigated 30 years ago, the last few years have brought about a renaissance in their chemistry. This Review highlights the most recent developments regarding ring opening, cycloadditions, and ring enlargement.
How has the European Commission designed its new enlargement methodology in times of enlargement fatigue? Several studies have pointed out the French opposition to launching accession negotiation ...with North Macedonia and Albania in 2019 as a significant factor explaining the content of the new methodology. Traditionally, enlargement policy has been seen through the lenses of rational choice institutionalism: from this perspective, the new methodology would be resulting from such an external shock. This paper argues instead, using the discursive institutionalism framework and the concept of institutional bricolage, that the new methodology is the product of four different discourses on enlargement layered on top of each other.
Une réaction au « non » français ? Ou un exemple de bricolage institutionnel ?
Comment la Commission européenne a-t-elle conçu sa nouvelle méthodologie d'élargissement malgré une certaine lassitude face à ce processus ? Plusieurs études ont montré que l'opposition française au lancement des négociations d'adhésion avec la Macédoine du Nord et l'Albanie en 2019 expliquait le contenu de la nouvelle méthodologie. Traditionnellement, la politique d'élargissement a été vue à travers le prisme de l´institutionnalisme rationnel : de ce point de vue, la nouvelle méthodologie serait le résultat d’un tel choc externe. Cet article soutient au contraire, en utilisant le cadre de l'institutionnalisme discursif et le concept de bricolage institutionnel, que la nouvelle méthodologie est le produit de quatre discours différents sur l'élargissement superposés les uns sur les autres.
Since the dual fermion condensate be used to describe the center symmetry Z, we extend it to thermal QED3 and study the deconfinement phase transition by the truncated Dyson-Schwinger equation for ...the massive fermion propagator at finite temperature. We show that, for a massive fermion, the system first appears as a deconfinement phase transition with the increase of temperature and then the chiral symmetry is restored and the corresponding temperature of the deconfinement phase transition increases with the enlargement of the fermion mass. It should be pointed out here that the results obtained in this paper are not model independent but are heavily dependent on the truncated Dyson-Schwinger equation we have chosen.
This work deals with estimating the dominant size enlargement mechanism in spray fluidized beds. A new process model is presented, which consists of population balances and a heat‐ and mass‐transfer ...model. New methods to incorporate the wet surface fraction and the Stokes criterion are proposed, which allow for the probability of wet collisions and the probability of successful wet collisions to be calculated. The product of these parameters, the probability of successful collisions, is linked to the dominant size enlargement mechanism. Simulation studies were performed to investigate the influence of inlet gas temperature, viscosity, droplet size, and contact angle on the probability of successful collisions. Further simulation results based on experiments available in literature suggest that exceeding a probability of successful collisions of 0.001 is sufficient for agglomeration to become dominant. Otherwise, layering will be the dominant size enlargement mechanism. Finally, regime maps of layering and agglomeration are constructed.
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