Ortho Para Substitution
Ortho Para Substitution - Related Videos
01:14
Directing Effect of Substituents: ortho–para-Directing Groups
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2025
Ortho–para directors are substituent groups attached to the benzene ring and direct the addition of an electrophile to the positions ortho or para to the substituent. All electron-donating groups are considered ortho–para directors. They donate electrons to the ring and make the ring more electron-rich. The ring is therefore susceptible to the addition of electrophiles. Substituents such as amino, hydroxy, or alkoxy, containing lone pairs on the atom adjacent to the ring, donate electrons...
01:24
ortho–para-Directing Deactivators: Halogens
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2023
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
01:11
ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
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2025
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
08:43
Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives
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2016
An operationally simple procedure for the synthesis of ortho-trifluoromethoxylated aniline derivatives via a two-step sequence of O-trifluoromethylation of N-aryl-N-hydroxyacetamide followed by thermally induced intramolecular OCF3-migration is reported.
14:21
Nucleophilic Substitution
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2023
Source: Vy M. Dong and Daniel Kim, Department of Chemistry, University of California, Irvine, CA Nucleophilic substitution reactions are among the most fundamental topics covered in organic chemistry. A nucleophilic substitution reaction is one where a nucleophile (electron-rich Lewis base) replaces a leaving group from a carbon atom. SN1 (S = Substitution, N = Nucleophilic, 1 = first-order kinetics) SN2 (S = Substitution, N = Nucleophilic, 2 = second-order kinetics) This video will help to...
FAQs
Electron-donating groups influence which sigma-complex pathways are most favorable during electrophilic aromatic substitution. The temporary intermediate is resonance-stabilized, and substitution at positions adjacent or opposite to the existing group commonly receives this preference. This relationship allows chemists to anticipate regioselectivity, meaning the relative formation of products with different substituent positions.
Halogens demonstrate that directing preference and overall reactivity are separate features of aromatic substitution. Although halogen substitution reduces the ring’s reactivity toward electrophilic aromatic substitution, halogen-substituted rings still favor new groups at ortho and para positions. Recognizing this distinction prevents the incorrect assumption that a deactivating substituent must direct substitution elsewhere.
The sigma complex provides the key mechanistic comparison between possible substitution positions. An electrophile temporarily bonds to the aromatic ring, producing a resonance-stabilized intermediate whose stability varies with the existing substituent and the location of new bond formation. More favorable stabilization helps explain why one positional pathway can dominate, although product mixtures may still result.
Ortho Para Substitution requires evaluating the existing substituent’s influence rather than treating all ring positions as equivalent. The substituent changes the relative favorability of sigma-complex formation, so adjacent and opposite positions may become preferred. This approach connects mechanism with product prediction: the expected outcome depends on directing behavior, ring reactivity, and the possibility of multiple positional products.
Begin by identifying the substituent already attached to the benzene ring, then determine whether it commonly promotes ortho and para substitution. Mark the adjacent and opposite positions as the principal candidates and consider whether both can produce products. This workflow helps anticipate regioselectivity and alerts the chemist to possible mixtures before evaluating a synthetic route.
The directing pattern can help chemists select a substituted aromatic starting material and predict where a later electrophilic substitution will introduce a new group. Choosing a ring arrangement that places the desired site in an ortho or para relationship may improve planning and reduce uncertainty. The predicted positional products can then guide interpretation of the reaction outcome.
The observed product distribution provides evidence about how the existing substituent influenced electrophilic aromatic substitution. Identifying whether new groups appear mainly at adjacent or opposite positions helps assess regioselectivity and compare the result with the expected directing pattern. A mixture can also show that more than one favorable ring position remained available during the reaction.