why is the benzene ring not readily attacked by bromine? thanks

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ah4p
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thnks i appreciate any help
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thymolphthalein
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I believe it's because addition reactions of benzene require high activation energy and it destabilizes the benzene ring.

However, benzene can undergo substitution reactions as it preserves the delocalised pi electron system and is feasible energetically.
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charco
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(Original post by ah4p)
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thnks i appreciate any help
As above re: addition reactions.

Halogenation (electrophilic substitution) of the benzene ring requires a Friedel-Crafts type catalyst (usually iron, which forms FeBr3 in situ) as the bromine molecule is non-polar
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ah4p
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(Original post by thymolphthalein)
I believe it's because addition reactions of benzene require high activation energy and it destabilizes the benzene ring.

However, benzene can undergo substitution reactions as it preserves the delocalised pi electron system and is feasible energetically.
(Original post by charco)
As above re: addition reactions.

Halogenation (electrophilic substitution) of the benzene ring requires a Friedel-Crafts type catalyst (usually iron, which forms FeBr3 in situ) as the bromine molecule is non-polar

thank you
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carrotstar
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Look at the structure of the benzene ring. There are 6 bonds which appear to have properties halfway between single and double bonds - hence why it can be drawn in two ways (6 equal bond lengths, or alternating single/double bonds). This makes them completely unique, and is caused by the way that electrons are shared in the molecule.

Because there are so many electrons involved in bonding so close together, they are 'delocalised' over the ring. This means they are constantly moving around, are shared between all C atoms, and can be anywhere around the ring at any time, creating a more stable structure.

Because the structure is so stable, it is challenging for any reaction to take place, so a very high activation enthalpy and a very reactive chemical is required to make any impression.

This means that more must be present than a weak bromine atom (or atoms) to affect the benzene ring's stability.
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ah4p
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(Original post by carrotstar)
Look at the structure of the benzene ring. There are 6 bonds which appear to have properties halfway between single and double bonds - hence why it can be drawn in two ways (6 equal bond lengths, or alternating single/double bonds). This makes them completely unique, and is caused by the way that electrons are shared in the molecule.

Because there are so many electrons involved in bonding so close together, they are 'delocalised' over the ring. This means they are constantly moving around, are shared between all C atoms, and can be anywhere around the ring at any time, creating a more stable structure.

Because the structure is so stable, it is challenging for any reaction to take place, so a very high activation enthalpy and a very reactive chemical is required to make any impression.

This means that more must be present than a weak bromine atom (or atoms) to affect the benzene ring's stability.

thakn you
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Infraspecies
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The electron density isn't sufficiently large.
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