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15 Cards in this Set
- Front
- Back
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When a benzene ring attacks an electrophile it adds the Electrophile to the dbl bond resulting in a carbocation transition state known as
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Sigma complex
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The sigma complex is/is not aromatic. why?
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NOT.
break in the conjugation of sp2 carbons. One carbon now becomes sp3 hybridized. |
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Electrophillic aromatic substitution
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the substitution of a hydrogen proton with an electrophile (and regeneration of aromaticity).
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Bromination of benzene requires:
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FeBr3/Br2
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Rate determining step of Electrophillic aromatic substitution
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formation of the sigma complex (b/c of loss of aromaticity)
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The second step of the mechanism is exothermic b/c:
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aromaticity is reobtained.
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Reagent for Chlorination of benzene
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ALCl3/ Cl2
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Reagents required for iodination of benzene
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I2/ HNO3
(to oxidize/used up in rxn) |
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Nitration of benzene requires:
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HNO3/H2SO4
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Sulfonation of benzene requires:
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SO3/H2SO4
SO3 good electrophile (w/ 4 resonance structures) |
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Desulfonation of Benzenesulfonic acid requires
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H+/ heat
(follows the same mechanism as sulfonation in reverse) |
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Ortho-para directors
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O- > R-N-R > OH > -OR > anilides> -R (no lone pairs) > Halogens
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Meta directors
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Nitro > cyano > SO3H > ketones > aldehydes > carboxyllic acids
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Halogens are
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Electron withdrawing by inductive effects but donating by resonance. Resonance > induction and therfore halogens are ortho-para directors.
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when activating and deactivating groups counter eachother in where to place substituents...
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the activating group (ortho-para usually wins)
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