Chap06 - Aromatics Three alkenes living next door to each...

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Aromatics Three alkenes living next door to each other in a 6-membered ring form a really special supersafe community known as a benzene ring. Organic compounds with benzene rings in their structures known as aromatics . Each carbon forms 1.5 bonds (3 shared electrons) with each of its two neighbor carbons in the ring. How???? The first C-C bond between neighbors is an ordinary sigma (single) bond (2 electrons). This bond is pretty safe from attack by acids like most sigma bonds. The remainder of the C-C bonds between carbon neighbors in the ring community are pi bonds. Their electrons live outside of the
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space between atoms, and are vulnerable to attack by predatory acids.
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To solve this problem benzene's carbons make a contract: everyone pools their pi electrons and everybody is responsible for the safety of all six of these pi electrons. Each ring carbon shares an average of one pi electron (1/2 of a bond) with each of its two neighbors in the ring. There are no single or double bonds in benzene. Pi electrons are allowed to roam freely throughout the ring community but are fiercely guarded by the community as a whole. Billionaire carbon says to neighbors- “What's mine is yours, just keep it away from the riff- raff!" Benzene says: "Circle the wagons- there are hostile acids out there seeking our pi electrons!"
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C H C H C H CH CH C H C H C H C H CH CH C H The structure on the left or right is what the three alkene community would look like without the pi electron contract. Benzene is so stable that Br 2 (bromine, a really nasty electrophile), which normally eats pi electrons in alkenes in milliseconds, is unable to react with it without the help of a catalyst!
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Chap06 - Aromatics Three alkenes living next door to each...

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