For instance, among N-chlorosuccinimide, N-bromosuccinimide and N-iodosuccinimide, which one would give most feasible respective halogenated product once reacted with an aromatic?
Following the order of electronegativity the oxidation potentials and hence free energy change of the reagent which drives the reaction could be a good predictor of success in electrophilic aromatic substitution.
This would suggest as previously stated Cl>Br>I.
However from a kinetic perspective the polarisation of the Halide-succinimide bond is important in establishing a low energy transition state. This can be estimated to an extent by the ease of ionisation of the N-X bond which has the inverse reactivity I>Br>Cl.
Which of these effects dominates can be strongly influenced by the nature of the aromatic ring in question and is complicated by radical mechanisms in the presence of light.
In practice, I find the bromination tends to be a more facile reaction in general.
Following the order of electronegativity the oxidation potentials and hence free energy change of the reagent which drives the reaction could be a good predictor of success in electrophilic aromatic substitution.
This would suggest as previously stated Cl>Br>I.
However from a kinetic perspective the polarisation of the Halide-succinimide bond is important in establishing a low energy transition state. This can be estimated to an extent by the ease of ionisation of the N-X bond which has the inverse reactivity I>Br>Cl.
Which of these effects dominates can be strongly influenced by the nature of the aromatic ring in question and is complicated by radical mechanisms in the presence of light.
In practice, I find the bromination tends to be a more facile reaction in general.
N-bromosuccinimde will give best results. Br is more selective than Cl.
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