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In chemistry, initiation is a chemical reaction that triggers one or more secondary reactions. Initiation creates a reactive centre on a molecule which produces a chain reaction . [ 1 ] The reactive centre generated by initiation is usually a radical , but can also be cations or anions . [ 2 ]
In the reaction, thermal or photochemical decomposition of N-halogenated amine 1 in the presence of a strong acid (concentrated sulfuric acid or concentrated CF 3 CO 2 H) generates a nitrogen radical intermediate. The radical then abstracts an intramolecular hydrogen atom to give a cyclic amine 2 (pyrrolidine or, in some cases, piperidine).
The problem of heat transfer is compounded by the highly exothermic nature of free radical addition polymerization. The polymerization is obtained with a broad molecular weight distribution due to the high viscosity and lack of good heat transfer. very high molecular weights are obtained. Gel effect.
Diverse methods are employed to manipulate the initiation, propagation, and termination rates during chain polymerization. A related issue is temperature control, also called heat management, during these reactions, which are often highly exothermic. For example, for the polymerization of ethylene, 93.6 kJ of energy are released per mole of ...
Protein folding problem: Is it possible to predict the secondary, tertiary and quaternary structure of a polypeptide sequence based solely on the sequence and environmental information? Inverse protein-folding problem: Is it possible to design a polypeptide sequence which will adopt a given structure under certain environmental conditions?
High energy initiation refers to the generation of chain carriers by radiation. Chemical initiation is due to a chemical initiator. For the case of radical polymerization as an example, chain initiation involves the dissociation of a radical initiator molecule (I) which is easily dissociated by heat or light into two free radicals (2 R°).
In the simplest example oxygen can be used as it exists naturally in its triplet state (i.e. it is a diradical). This is referred to as air inhibition and is a diffusion-controlled reaction with rates typically in the order of 10 7 –10 9 mol −1 s −1 , [ 3 ] the resulting peroxy radicals (ROO•) are less reactive towards polymerisation.
For chain-growth polymerization, the overall activation energy is = +, where i, p and t refer respectively to initiation, propagation and termination steps. The propagation step normally has a very small activation energy, so that the overall value is negative if the activation energy for termination is larger than that for initiation.