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Growth, Exfoliation, and Synthesis
Published in Yongqing Cai, Gang Zhang, Yong-Wei Zhang, Phosphorene, 2019
As a new and important 2D material, the growth and fabrication of phosphorene have been extensively exploited, which are essential for using the superior properties of black phosphorus (BP) in practical applications. Referring to the synthesis of other 2D materials such as graphene and transition metal dichalcogenides (TMDs), phosphorene can be fabricated via two routes: bottom-up methods and top-down methods. First, we will comment these fabrication methods and discuss their applicability for obtaining phosphorene. As typical bottom-up methods, the development of wafer-scale synthesis methods via chemical vapor deposition (CVD) on metal substrates and epitaxial growth on insulating substrates has enabled large-scale device fabrication based on graphene and TMDs.7 However, direct chemical growth strategies for phosphorene are still lacking at present, probably due to its chemically active surface that is fragile when exposed to air, as well as the absence of a suitable substrate for its CVD growth. Its development and implementation will require concerted efforts from the materials and chemistry communities.
Other Nonnitrogenous Organocatalysts
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
Dioxirane-mediated epoxidations are stereospecific and appear to pass through a concerted, though possibly asynchronous,16,17 transition state. Two transition states have been proposed: planar transition state 12P and spiro transition state 12S (Figure 8.7). By analyzing kinetic data of various substituted alkenes, Baumstark and coworkers proposed that DMDO prefers to react through a spiro transition state.18 This is due to the observation that some cis-alkenes (R1, R2 = H) can be up to 20 times more reactive than the corresponding trans-alkene (R1, R4 = H). Several computational studies also indicate that a spiro transition state is favored for epoxidations with both DMDO16,19 and fluorinated dioxiranes.20
Atom Economy
Published in Aidé Sáenz-Galindo, Adali Oliva Castañeda-Facio, Raúl Rodríguez-Herrera, Green Chemistry and Applications, 2020
Kunnambeth M. Thulasi, Sindhu Thalappan Manikkoth, Manjacheri Kuppadakkath Ranjusha, Padinjare Veetil Salija, Nisha Vattakkoval, Shajesh Palantavida, Baiju Kizhakkekilikoodayil Vijayan
Pericyclic reactions are concerted reactions in which reorganization of electrons occur via a single cyclic transition state. There are different types of pericyclic reactions, such as cycloaddition, electrocyclic reaction, sigmatropic rearrangement, group transfer reaction, chelotropic reaction and diatropic rearrangement. Pericyclic reactions are 100% atom economical, like simple addition and rearrangement.
Reactive atomistic simulations of Diels-Alder-type reactions: conformational and dynamic effects in the polar cycloaddition of 2,3-dibromobutadiene radical ions with maleic anhydride
Published in Molecular Physics, 2021
Uxía Rivero, Haydar Taylan Turan, Markus Meuwly, Stefan Willitsch
Since two bonds are formed in this reaction, questions pertaining to its concertedness and synchronicity are central to the understanding of the reaction mechanism. A reaction is considered to be concerted if the reaction pathway exhibits only a single transition state (TS) between reactants and products so that it occurs in a single step. By contrast, a stepwise mechanism involves several transition states which have to be traversed between the reactants and the products. The time elapsed between formation of the first and the second bond defines the synchronicity of the process [15]. A synchronous process is necessarily concerted, but an asynchronous one can be concerted or stepwise depending on the presence or absence of intermediates. As an important implication, only the s-cis-conformer of the diene can react in a synchronous DA reaction, whereas both the s-cis and s-trans conformational isomers can in principle be reactive in a stepwise mechanism.