Dolbier HW Solutions 288

Dolbier HW Solutions 288 - functional group and the other...

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12.11 The compounds shown all undergo electrophilic aromatic substitution more slowly than benzene. Therefore, @ CH 2 Cl, @ CHCl 2 , and @ CCl 3 are deactivating substituents. The electron-withdrawing power of these substituents, and their tendency to direct incoming elec- trophiles meta to themselves, will increase with the number of chlorines each contains. Thus, the substituent that gives 4% meta nitration (96% ortho 1 para) contains the fewest chlorine atoms ( G CH 2 Cl), and the one that gives 64% meta nitration contains the most ( @ CCl 3 ). 12.12 ( b ) Attack by bromine at the position meta to the amino group gives a cyclohexadienyl cation in- termediate in which delocalization of the nitrogen lone pair cannot participate in dispersal of the positive charge. ( c ) Attack at the position para to the amino group yields a cyclohexadienyl cation intermediate that is stabilized by delocalization of the electron pair of the amino group. 12.13 Electrophilic aromatic substitution in biphenyl is best understood by considering one ring as the
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Unformatted text preview: functional group and the other as a substituent. An aryl substituent is ortho, para-directing. Nitration of biphenyl gives a mixture of o-nitrobiphenyl and p-nitrobiphenyl. 12.14 ( b ) The carbonyl group attached directly to the ring is a signal that the substituent is a meta-directing group. Nitration of methyl benzoate yields methyl m-nitrobenzoate. HNO 3 H 2 SO 4 Methyl benzoate COCH 3 O Methyl m-nitrobenzoate (isolated in 81 – 85% yield) O 2 N COCH 3 O HNO 3 H 2 SO 4 O 2 N o-Nitrobiphenyl (37%) Biphenyl NO 2 p-Nitrobiphenyl (63%) 1 NH 2 1 1 NH 2 1 NH 2 1 NH 2 Br H Br H Br H Br H NH 2 1 Br H NH 2 1 NH 2 1 Br H Br H Deactivating, ortho, para-directing CH 2 Cl Deactivating, ortho, para-directing CHCl 2 Deactivating, meta-directing CCl 3 Benzyl chloride CH 2 Cl (Dichloromethyl)benzene CHCl 2 (Trichloromethyl)benzene CCl 3 282 REACTIONS OF ARENES: ELECTROPHILIC AROMATIC SUBSTITUTION...
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This note was uploaded on 09/26/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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