Electrophilic Halogen Attack
Electrophilic Halogen Attack - Related Videos
02:38
Electrophilic Addition to Alkynes: Halogenation
0 Views •
2025
Introduction Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide. Reaction Mechanism In the first step, a π bond...
03:01
Halogens
0 Views •
2020
Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. Astatine is a highly unstable radioactive element, so currently, most of its properties are unknown due to its short half-life. Tennessine is a synthetic element also predicted to be in this group. The halogens are not found as single atoms but exist as diatomic molecules. The atomic radius increases from fluorine to iodine. The valence shell...
06:44
From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
0 Views •
Cited by 2 •
2018
A protocol for the synthesis of a new type of mesogens, based on the halogen-bonded supramolecular anion [CnF2n+1-I···I···I-CnF2n+1]−, is reported.
02:28
Electrophiles
0 Views •
2023
This lesson explains the definition, classification, and characteristic features of an electrophile that are key features of nucleophilic substitution reactions. An analysis of their charge and orbital picture helps understand their reactivity for seeking electrons. Electrophiles can be classified into positive and neutral species. Other classes include free radicals and polar functional groups. While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...
01:21
Acid Attack on Concrete
0 Views •
2024
When acids come into contact with concrete, they initiate a chemical reaction that dissolves the hydrated cement paste. This process leads to softening and structural weakening of the concrete. This issue is commonly observed in environments such as chimneys, sewers, and industrial settings. The severity of the damage increases as the pH of the water interacting with the concrete drops below 6.5. In particular, a pH under 4.5 can cause significant concrete damage. The rate at which hydrogen...
FAQs
The key mechanistic step is polarization of the halogen reagent, which creates an electron-deficient halogen species. That electrophile is attracted to an electron-rich region of the aromatic molecule and can form a new carbon-halogen bond. The reaction therefore depends on both the reagent’s polarization and the availability of electron density within the aromatic system.
The sigma complex is the temporary intermediate formed after the electrophilic halogen bonds to the aromatic ring. During this stage, the ring no longer has its fully restored aromatic arrangement. Loss of a proton from the intermediate then reestablishes aromaticity, making the sigma complex a central link between bond formation and the final halogenated product.
Substituents change how electron density is distributed across a benzene derivative. This distribution influences how readily an electrophilic halogen can attack and which ring position is favored. Consequently, substituents can affect both reaction rate and regioselectivity, meaning the preferred location of halogen incorporation. These effects help explain different outcomes among aromatic substrates.
Chlorine and bromine can serve as the halogen introduced into an aromatic compound through this reaction pattern. The specific halogen determines which carbon-halogen bond appears in the product, while the aromatic substrate and its substituents influence the favored position. This makes electrophilic halogen attack useful for preparing differently halogenated benzene derivatives.
A general sequence begins with a polarized halogen reagent generating an electrophilic halogen. The electrophile then bonds to an electron-rich site on the aromatic ring, producing a temporary sigma complex. Finally, proton loss restores aromaticity and yields the halogenated aromatic compound. This sequence connects reagent activation, temporary loss of aromaticity, and product formation.
The reaction is useful when a synthetic route requires chlorine, bromine, or another halogen on an aromatic framework. Halogenated benzene derivatives can serve as functionalized organic compounds for further route design, including work relevant to pharmaceuticals and materials. Substituent-controlled regioselectivity also helps chemists target a particular ring position during compound development.