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In a linear synthesis—often adequate for simple structures—several steps are performed sequentially until the molecule is complete; the chemical compounds made in each step are called synthetic intermediates. [1] Most often, each step in a synthesis is a separate reaction taking place to modify the starting materials.
This requires mixing the compounds in a reaction vessel, such as a chemical reactor or a simple round-bottom flask. Many reactions require some form of processing ("work-up") or purification procedure to isolate the final product. [1] The amount produced by chemical synthesis is known as the reaction yield.
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical reaction occurs. [1] A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases.
Synthesis of saturated fatty acids via fatty acid synthase II in E. coli. Straight-chain fatty acid synthesis occurs via the six recurring reactions shown below, until the 16-carbon palmitic acid is produced. [2] [3] The diagrams presented show how fatty acids are synthesized in microorganisms and list the enzymes found in Escherichia coli. [2]
This step is known as the ammonia synthesis loop: + The gases (nitrogen and hydrogen) are passed over four beds of catalyst, with cooling between each pass to maintain a reasonable equilibrium constant. On each pass, only about 15% conversion occurs, but unreacted gases are recycled, and eventually conversion of 97% is achieved.
In chain-growth (or chain) polymerization, the only chain-extension reaction step is the addition of a monomer to a growing chain with an active center such as a free radical, cation, or anion. Once the growth of a chain is initiated by formation of an active center, chain propagation is usually rapid by addition of a sequence of monomers.
This synthesis took a total of 31 steps and proceeded in 0.06% overall yield. The hydrocodone synthesis of Kenner C. Rice is one of the most efficient and proceeds in 30% overall yield in 14 steps. [4] At 9 steps, the Barriault route is the shortest to date, but contains a number of low-yielding steps and is racemic. [5]
Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations , which symbolically present the starting materials, end products, and sometimes intermediate products ...