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The electrophilic Br-Br molecule interacts with electron-rich alkene molecule to form a π-complex 1. Forming of a three-membered bromonium ion The alkene is working as an electron donor and bromine as an electrophile. The three-membered bromonium ion 2 consisted of two carbon atoms and a bromine atom forms with a release of Br −.
Bond energies to bromine tend to be lower than those to chlorine but higher than those to iodine, and bromine is a weaker oxidising agent than chlorine but a stronger one than iodine. This can be seen from the standard electrode potentials of the X 2 /X − couples (F, +2.866 V; Cl, +1.395 V; Br, +1.087 V; I, +0.615 V; At, approximately +0.3 V).
Therefore, they are generated by adding iron filings to bromine or chlorine. Here is the mechanism of this reaction: The mechanism for bromination of benzene. The mechanism for iodination is slightly different: iodine (I 2) is treated with an oxidizing agent such as nitric acid to obtain the electrophilic iodine ("I +", probably IONO 2).
The bromine electrophile is generated by diatomic bromine or another source such as potassium bromide, which can be oxidized to generate bromine in situ by the peracetic acid. The source of the mercuric ion is mercuric acetate , and this reagent is mixed with peracetic acid in AcOH to provide the oxidizing conditions.
The nitration of benzene is achieved via the action of the nitronium ion as the electrophile. The sulfonation with fuming sulfuric acid gives benzenesulfonic acid. Aromatic halogenation with bromine, chlorine, or iodine gives the corresponding aryl halides. This reaction is typically catalyzed by the corresponding iron or aluminum trihalide.
The bromide ion acquires a positive formal charge. At this moment the halogen ion is called a "bromonium ion" or "chloronium ion", respectively. When the first bromine atom attacks the carbon–carbon π-bond, it leaves behind one of its electrons with the other bromine that it was bonded to in Br 2.
Bromine is more electronegative than carbon (2.9 vs 2.5). Consequently, the carbon in a carbon–bromine bond is electrophilic, i.e. alkyl bromides are alkylating agents. [2] Carbon–halogen bond strengths, or bond dissociation energies are of 115, 83.7, 72.1, and 57.6 kcal/mol for bonded to fluorine, chlorine, bromine, or iodine, respectively ...
Bromine is a chemical element; it has symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between those of chlorine and iodine.