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The reaction mechanism for an alkene bromination can be described as follows. In the first step of the reaction, a bromine molecule approaches the electron-rich alkene carbon–carbon double bond. The bromine atom closer to the bond takes on a partial positive charge as its electrons are repelled by the electrons of the double bond.
The same is true when an alkene reacts with water in an additional reaction to form an alcohol that involves carbocation formation. The hydroxyl group (OH) bonds to the carbon that has the greater number of carbon-carbon bonds, while the hydrogen bonds to the carbon on the other end of the double bond, that has more carbon–hydrogen bonds.
Illustrative of the bromination of an alkene is the route to the anesthetic halothane from trichloroethylene: [6] Iodination and bromination can be effected by the addition of iodine and bromine to alkenes. The reaction, which conveniently proceeds with the discharge of the color of I 2 and Br 2, is the basis of the analytical method.
A hydrohalogenation reaction is the electrophilic addition of hydrogen halides like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes. [ 1 ] [ 2 ] [ 3 ] If the two carbon atoms at the double bond are linked to a different number of hydrogen atoms, the halogen is found preferentially at the carbon with fewer ...
The reaction is considered Markovnikov as it results in water addition with same regiospecificity as a direct hydration reaction. Alkene hydroboration-oxidation: Stereospecific: Can only be syn addition – hydrogen and hydroxyl (-OH) are added to the same face. The reaction is anti-Markovnikov. Hydroxyl attaches to the less substituted carbon.
The simplest halonium ions are of the structure H− + −H (X = F, Cl, Br, I). Many halonium ions have a three-atom cyclic structure, similar to that of an epoxide, resulting from the formal addition of a halogenium ion X + to a C=C double bond, as when a halogen is added to an alkene. [1]
An old qualitative test for the presence of the alkene functional group is that alkenes turn brown aqueous bromine solutions colourless, forming a bromohydrin with some of the dibromoalkane also produced. The reaction passes through a short-lived strongly electrophilic bromonium intermediate. This is an example of a halogen addition reaction. [18]
The initial step of the halogenation of aromatic compounds differs from that of the halogenation of alkenes in that alkenes do not require a catalyst to enhance the electrophilicity of the halogen. The formation of the arenium ion results in the temporary loss of aromaticity , which has a higher activation energy compared to halonium ion ...