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In chemistry, chain propagation (sometimes just referred to as propagation) is a process in which a reactive intermediate is continuously regenerated during the course of a chemical chain reaction. For example, in the chlorination of methane , there is a two-step propagation cycle involving as chain carriers a chlorine atom and a methyl radical ...
The chain length is defined as the average number of times the propagation cycle is repeated, and equals the overall reaction rate divided by the initiation rate. [ 1 ] Some chain reactions have complex rate equations with fractional order or mixed order kinetics.
Chain initiation is the initial generation of a chain carrier, which is an intermediate such as a radical or an ion which can continue the reaction by chain propagation. Initiation steps are classified according to the way that energy is provided: thermal initiation, high energy initiation, and chemical initiation, etc. Thermal initiation uses ...
In the propagation phase, the lipid radical reacts with oxygen (O 2) or a transition metal, forming a peroxyl radical (LOO •). This peroxyl radical continues the chain reaction by reacting with a new unsaturated fatty acid, producing a new lipid radical (L •) and lipid hydroperoxide (LOOH). These primary products can further decompose into ...
A chain reaction is an example of a complex mechanism, in which the propagation steps form a closed cycle. In a chain reaction, the intermediate produced in one step generates an intermediate in another step. Intermediates are called chain carriers. Sometimes, the chain carriers are radicals, they can be ions as well.
The growing chain will react with molecular oxygen, producing an oxygen radical, which is much less reactive (Figure 17). This significantly slows down the rate of propagation. Figure 17: Inhibition of polystyrene propagation due to reaction of polymer with molecular oxygen.
The termination step can vary, in both its actual chemical reaction and when it will occur. [6] Lipid peroxidation is a self-propagating chain reaction and will proceed until the lipid substrate is consumed and the last two remaining radicals combine, or a reaction which terminates it occurs. [3]
In which I + is the initiator, M is the monomer, M + is the propagating center, and , , , and are the rate constants for initiation, propagation, termination, and chain transfer, respectively. [ 5 ] [ 6 ] [ 12 ] For simplicity, counterions are not shown in the above reaction equations and only chain transfer to monomer is considered.