China 
Africa 
Explore chapters and articles related to this topic
Inorganic Carbon: Modeling
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Global Resources and Universal Processes, 2020
Leslie D. McFadden, Ronald G. Amundson
During weathering, parent material carbonate undergoes dissolution and reprecipitation in the soil. The carbon (13C/12C,14C/12C) and oxygen (18O/16O) isotope ratios of pedogenic carbonate that forms from dust or parent material carbonate, or from Ca2+ derived from silicate weathering, are determined by isotopic composition of soil CO2 and H2O. These are the primary carbon and oxygen reservoirs, respectively, for the carbonate. Therefore, pedogenic carbonate reflects only isotopic conditions of the soil and bears no memory of the isotopic composition of the rock or mineral from which it was derived.
Alkenes and Alkynes: Structure, Nomenclature, and Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
3,3-Dimethylpent-1-ene initially reacts with the proton of HBr to give a secondary carbocation, A. Only atoms or groups of the carbon atoms attached to C+ can migrate, leading to a rearrangement. A hydrogen atom is available on the adjacent primary carbon and also on the adjacent tertiary carbon. If the hydrogen atom moves from the primary carbon, a less stable primary carbocation will result, and such a reaction to give a less stable product will not occur because it is an endothermic process. However, if the hydrogen atom moves from C3, the tertiary carbon, the product is a more stable tertiary carbocation, B. This reaction of a hydrogen atom moving to an adjacent carbon to give a more stable carbocation is called a 1,2-hydride shift and represented by the “curly” arrow shown. The mechanism shown involves drawing the starting material, the final product, and all intermediates. Why does a rearrangement occur before the nucleophile can react with C+?
The Polymeric Matrix and its Influence
Published in Maik W. Jornitz, Theodore H. Meltzer, Sterile Filtration, 2020
Maik W. Jornitz, Theodore H. Meltzer
Consider again the polymer dissolved in a good solvent, the first step in preparing the casting formulation. Its chains are extended. As the pore former or nonsolvent is added in the second step in conformity with the requirements of the casting formulation, the solution will progressively become a poorer and poorer solvent for the polymer. The polymer chains will contract from their extended positions and will become increasingly more coiled. In this two-step process (called let-down), they will become tangled and intertwined even before solvent evaporation is commenced. This will continue until phase inversion occurs and a wet gel forms. At this point, further substantial segmental space adjustment becomes halted by the high viscosity of the wet gel. The finished membrane will have tensile and elongational properties that reflect the prior two-step chain entangling. When a specimen of this film is pulled in a tensile strength and elongation test machine, its rupture will require the breaking of tangled molecular strands. At the molecular level, the rupture of strong primary carbon-carbon covalent bonds will be involved. Disentanglement by the easy chain slippage involving the weaker van der Waals bonds will be limited by the intertwining of the long molecules. Therefore, the yield to break, the percent elongation of the specimen, will be relatively low. The tensile strength, the amount of load needed to break the tangled chains, will be relatively high, reflecting chain breakage rather than slippage.
Iodination of vanillin and subsequent Suzuki-Miyaura coupling: two-step synthetic sequence teaching green chemistry principles
Published in Green Chemistry Letters and Reviews, 2019
James J. Palesch, Beau C. Gilles, Jared Chycota, Moriana K. Haj, Grant W. Fahnhorst, Jane E. Wissinger
Continuing with our efforts to revise the organic chemistry laboratory curriculum to demonstrate modern green synthetic methods, we sought to replace our program’s decades-old electrophilic aromatic substitution (EAS) reaction and Grignard synthesis with more environmentally-friendly chemistries. These classes of reactions are important topics to include in both organic chemistry lecture and laboratory courses. EAS reactions are invaluable synthetic tools for functionalizing aromatic compounds, and the Grignard reaction has historically been a primary carbon–carbon bond forming reaction. Though there are reported green replacements for each of these types of reactions (1), we sought to develop novel experiments which would complement our current curriculum with specific learning outcomes related to guided-inquiry pedagogy, spectroscopic analysis, laboratory techniques used, green chemistry principles, and scalability for the large teaching laboratory environment.