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Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at themeta position are calledmetadirectors. All metadirectors either havea positive charge on the atom directly bonded to the ring or a partial positive charge. These groups function by withdrawing electrons from the ring through inductive and resonance effects. Consider the carbocation intermediates formed upon the addition of an electrophile on nitrobenzene at the ortho, meta, and para positions. While all three haveresonance forms,the ortho and para intermediates haveone unfavorable structure eachdue to repelling positive charges onadjacent atoms. However, adjacent atoms do not bear like charges in any of the resonance forms of themetaintermediates. Consequently, the ortho- and para-carbocation intermediates are less stable than themeta-carbocation intermediates. Therefore, substitution ispreferred at the meta position.

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Meta directingSubstituentsBenzene RingElectrophilic SubstitutionMeta directorsPositive ChargeInductive EffectsResonance EffectsCarbocation IntermediatesOrthoMetaParaRepelling Positive ChargesMeta carbocationMeta substitution

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18.13 : Directing Effect of Substituents: meta-Directing Groups

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18.1 : 벤젠 유도체의 NMR 분광법

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18.2 : 벤질산 위치에서의 반응: 산화 및 환원

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18.3 : 벤질산 위치에서의 반응 : 할로겐화

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18.4 : 친전자성 방향족 대체: 개요

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18.5 : 친전자성 방향족 치환: 벤젠의 염소화 및 브롬화

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18.6 : 친전자성 방향족 치환: 벤젠의 불소화 및 요오드화

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18.7 : 친전자성 방향족 치환: 벤젠의 질화

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18.8 : 친전자성 방향족 치환: 벤젠의 설폰화

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18.9 : 친전자성 방향족 치환: Friedel–Crafts 벤젠의 알킬화

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18.10 : 친전자성 방향족 치환: Friedel–Crafts 벤젠의 아실화

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18.11 : Friedel-Crafts 반응의 한계

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18.12 : 치환의 지시 효과: ortho-para-directing groups

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18.14 : 직교-파라-디렉팅 활성제: -CH3, -OH, -⁠NH2, -OCH3

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18.15 : ortho-para-directing Deactivators: 할로겐

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