{"id":1464,"date":"2017-10-12T14:16:03","date_gmt":"2017-10-12T14:16:03","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/?post_type=chapter&p=1464"},"modified":"2018-10-05T19:04:25","modified_gmt":"2018-10-05T19:04:25","slug":"aromatic-ions","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/chapter\/aromatic-ions\/","title":{"raw":"Aromatic Ions","rendered":"Aromatic Ions"},"content":{"raw":"
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Objectives<\/h3>\r\n
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\r\n\r\nAfter completing this section, you should be able to\r\n
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  1. use the H\u00fcckel 4n<\/em> + 2 rule to explain the stability of the cyclopentadienyl anion, the cycloheptatrienyl cation and similar species.<\/li>\r\n \t
  2. use the H\u00fcckel 4n<\/em> + 2 rule to determine whether or not a given unsaturated cyclic hydrocarbon anion or cation is aromatic.<\/li>\r\n \t
  3. draw the resonance contributors for the cyclopentadienyl anion, cation and radical, and similar species.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
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    Charged Aromatic Compounds<\/h3>\r\nCarbanions and carbocations may also show aromatic stabilization. Some examples are:\r\n

    \"annulen3.gif\"<\/a><\/p>\r\nThe three-membered ring cation has 2 $$\\pi$$-electrons and is surprisingly stable, considering its ring strain<\/a>. Cyclopentadiene is as acidic as ethanol, reflecting the stability of its 6 \u03c0-electron conjugate base. Salts of cycloheptatrienyl cation (tropylium ion) are stable in water solution, again reflecting the stability of this 6 $$\\pi$$-electron cation.\r\n\r\n<\/div>\r\n

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    Exercises<\/h3>\r\n
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    \r\n\r\n1.<\/strong>\r\n\r\nDraw the resonance structures for cycloheptatriene anion. Are all bonds equivalent? How many lines (signals) would you see in a H1<\/sup> C13<\/sup> NMR?\r\n\r\n2.<\/strong>\r\n\r\nThe following reaction occurs readily. Propose a reason why this occurs?\r\n\r\n\"\"\r\n\r\n<\/div>\r\n
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    Solutions<\/h3>\r\n1.<\/strong>\r\n\r\n[reveal-answer q=\"698738\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"698738\"]All protons and carbons are the same, so therefore each spectrum will only have one signal each.\r\n\r\n\"\"[\/hidden-answer]\r\n\r\n2.<\/strong>\r\n\r\n[reveal-answer q=\"550453\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"550453\"]The ring becomes aromatic with the addition of two electrons. Thereby obeying the 4n+2 rule.[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
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    Contributors<\/h3>\r\n