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The increasing order of diazotiation of aromatic compounds |
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Answer» The influence of substituents on the reactivity of aromatic compounds in an electrophilic aromatic SUBSTITUTION is discussed below. The REACTION rate of a multistep reaction is DETERMINED by the activation energy of the slowest individual step, which is called the rate-determining step. The activation energy is the energy difference between the starting products of the respective step and its transition state. The reaction rate of electrophilic aromatic substitution therefore depends on the substituent's qualities, as these influence the transition state's energy. It is important to note that a substituent does not influence the starting product's energy in the same way. The activation energy and thus the reaction rate would otherwise not vary among different substituents. In the electrophilic aromatic substitution, the rate-determining step is USUALLY the formation of the σ complex. The σ complex resembles the transition state that is PASSED through when the the σ complex is formed from the starting products. This may be used as a basis for the following considerations of the substituent's influence on the reaction rate. Due to the transition state's extremely short lifetime, its structure cannot be experimentally determined. Thus, it is usually practically impossible to verify its structure. However, the fact that it can be estimated by the structure of the σ complex is quite an advantage. |
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