mechanism of addition of hydrogen Bromide to propene in presence of peroxide(with chemical reaction)
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Addition to symmetrical alkenes
A symmetrical alkene is one like ethene where the groups at both ends of the carbon-carbon double bond are the same.
The facts
The reaction happens at room temperature in the presence of organic peroxides or some oxygen from the air. Alkenes react very slowly with oxygen to produce traces of organic peroxides - so the two possible conditions are equivalent to each other.
The reaction is a simple addition of the hydrogen bromide. For example, with ethene:
With a symmetrical alkene you get exactly the same product in the absence of the organic peroxides or oxygen - but the mechanism is different.
The mechanism
Hydrogen halides (hydrogen chloride, hydrogen bromide and the rest) usually react with alkenes using an electrophilic addition mechanism. However, in the presence of organic peroxides, hydrogen bromide adds by a different mechanism.
Chain initiation
The chain is initiated by free radicals produced by an oxygen-oxygen bond in the organic peroxide breaking.
These free radicals extract a hydrogen atom from a hydrogen bromide molecule to produce bromine radicals.
Chain propagation
A bromine radical joins to the ethene using one of the electrons in the pi bond. That creates a new radical with the single electron on the other carbon atom.
That radical reacts with another HBr molecule to produce bromoethane and another bromine radical to continue the process.
Chain termination
Eventually two free radicals hit each other and produce a molecule of some sort. The process stops here because no new free radicals are formed.
A symmetrical alkene is one like ethene where the groups at both ends of the carbon-carbon double bond are the same.
The facts
The reaction happens at room temperature in the presence of organic peroxides or some oxygen from the air. Alkenes react very slowly with oxygen to produce traces of organic peroxides - so the two possible conditions are equivalent to each other.
The reaction is a simple addition of the hydrogen bromide. For example, with ethene:
With a symmetrical alkene you get exactly the same product in the absence of the organic peroxides or oxygen - but the mechanism is different.
The mechanism
Hydrogen halides (hydrogen chloride, hydrogen bromide and the rest) usually react with alkenes using an electrophilic addition mechanism. However, in the presence of organic peroxides, hydrogen bromide adds by a different mechanism.
Chain initiation
The chain is initiated by free radicals produced by an oxygen-oxygen bond in the organic peroxide breaking.
These free radicals extract a hydrogen atom from a hydrogen bromide molecule to produce bromine radicals.
Chain propagation
A bromine radical joins to the ethene using one of the electrons in the pi bond. That creates a new radical with the single electron on the other carbon atom.
That radical reacts with another HBr molecule to produce bromoethane and another bromine radical to continue the process.
Chain termination
Eventually two free radicals hit each other and produce a molecule of some sort. The process stops here because no new free radicals are formed.
darshanshree2003:
tq very much
thanks bro
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