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ortho–para-Directing Activators: –CH3, –OH, –&NoBreak;NH2, –OCH3

ortho–para-Directing Activators: –CH₃, –OH, –⁠NH₂, –OCH₃

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...

ortho–para-Directing Deactivators: Halogens

ortho–para-Directing Deactivators: Halogens

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...

meta-Directing Deactivators: –NO2, –CN, –CHO, –&NoBreak;CO2R, –COR, –CO2H

meta-Directing Deactivators: –NO₂, –CN, –CHO, –⁠CO₂R, –COR, –CO₂H

All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...

Directing Effect of Substituents: ortho–para-Directing Groups

Directing Effect of Substituents: ortho–para-Directing Groups

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...

Photochemical Electrocyclic Reactions: Stereochemistry

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation

Directing Effect of Substituents: meta-Directing Groups

Directing Effect of Substituents: meta-Directing Groups

Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at the meta position are called meta directors. All meta directors either have a 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...

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Related Experiment Video

Updated: Nov 4, 2025

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides CHIPS

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides CHIPS

Published on: June 20, 2014

Decoding Directing Groups and Their Pivotal Role in C-H Activation.

Karunanidhi Murali¹, Luana A Machado^1,2, Renato L Carvalho¹

¹Department of Chemistry, Federal University of Minas Gerais, Belo Horizonte, 31270-901, MG, Brazil.

Chemistry (Weinheim an Der Bergstrasse, Germany)

|May 26, 2021

Summary

This review details advancements in C-H functionalization, a key strategy in synthetic organic chemistry for drug discovery. It highlights novel metal and metal-free catalysts, directing groups, and photochemical methods for selective C-H bond activation.

Keywords:

C−H activation catalysis directing groups metals transition-metal catalysis

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Area of Science:

Synthetic organic chemistry
Catalysis
Medicinal chemistry

Background:

C-H functionalization is crucial for synthesizing complex molecules and drug discovery.
Traditional methods face challenges in selectivity and late-stage functionalization.
Emerging photo- and electrochemistry offer new pathways for C-H activation.

Purpose of the Study:

To provide a comprehensive overview of C-H bond activation strategies.
To discuss the fundamental science behind various metal and metal-free catalytic systems.
To highlight the role of directing groups and templates in achieving selective C-H functionalization.

Main Methods:

Review of existing literature on C-H functionalization.
Analysis of metal catalysts, metal-free ligands, and photochemical/electrochemical approaches.
Classification and discussion of directing groups and templates for selective C-H activation.

Main Results:

C-H functionalization enables efficient late-stage functionalization, simplifying total synthesis and drug development.
Development of novel metal and metal-free catalysts, including ligand-guided protocols.
Advancements in distal C-H bond activation through innovative templates and directing groups.
Increased focus on green chemistry principles, utilizing non-toxic metals and metal-free conditions.

Conclusions:

C-H activation is a powerful and versatile tool in modern synthetic chemistry.
The field continues to evolve with new catalytic systems and methodologies, including metal-free and directed approaches.
This review serves as a valuable resource for researchers seeking to understand and apply C-H activation strategies for selective functionalization.