Glossary of Organic Chemistry II

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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
Sigma complex
The sigma complex is/is not aromatic. why?
break in the conjugation of sp2 carbons. One carbon now becomes sp3 hybridized.
Electrophillic aromatic substitution
the substitution of a hydrogen proton with an electrophile (and regeneration of aromaticity).
Bromination of benzene requires:
Rate determining step of Electrophillic aromatic substitution
formation of the sigma complex (b/c of loss of aromaticity)
The second step of the mechanism is exothermic b/c:
aromaticity is reobtained.
Reagent for Chlorination of benzene
ALCl3/ Cl2
Reagents required for iodination of benzene
I2/ HNO3
(to oxidize/used up in rxn)
Nitration of benzene requires:
Sulfonation of benzene requires:

SO3 good electrophile (w/ 4 resonance structures)
Desulfonation of Benzenesulfonic acid requires
H+/ heat

(follows the same mechanism as sulfonation in reverse)
Ortho-para directors
O- > R-N-R > OH > -OR > anilides> -R (no lone pairs) > Halogens
Meta directors
Nitro > cyano > SO3H > ketones > aldehydes > carboxyllic acids
Halogens are
Electron withdrawing by inductive effects but donating by resonance. Resonance > induction and therfore halogens are ortho-para directors.
when activating and deactivating groups counter eachother in where to place substituents...
the activating group (ortho-para usually wins)

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