Related Experiment Video
Updated: May 18, 2026
06:44
From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Substituent effects in halogen bonding complexes between aromatic donors and acceptors: a comprehensive ab initio
Antonio Bauzá1, David Quiñonero, Antonio Frontera
1Departament de Química, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain.
Physical Chemistry Chemical Physics : PCCP
|October 14, 2011
Summary
Substituent effects on aromatic halogen bonds were studied. Electron-donating groups consistently strengthen these noncovalent interactions, regardless of their position, impacting interaction energies and bond order.
Area of Science:
- Computational Chemistry
- Supramolecular Chemistry
- Chemical Physics
Background:
- Halogen bonding is a crucial noncovalent interaction involving a Lewis acid (typically an electrophilic region on a halogen atom) and a Lewis base.
- Understanding substituent effects is key to tuning the strength and properties of halogen bonds in molecular recognition and materials science.
Purpose of the Study:
- To investigate how substituents on aromatic rings influence the energy of halogen bonding interactions.
- To compare the impact of substituents when the electron donor is within the aromatic ring (pyridine) versus outside the ring (cyanobenzene).
- To explore the role of electron density at the bond critical point as a measure of halogen bond order.
Main Methods:
- Quantum chemical calculations using the RI-MP2/aug-cc-pVDZ level of theory.
- Analysis of substituent effects using Hammett plots (interaction energies vs. Hammett's σ parameter).
- Application of Bader's "atoms-in-molecules" theory to analyze electron density.
Main Results:
- Substituent effects on interaction energies were found to be similar for both pyridine and cyanobenzene systems.
- Good linear correlations were observed between interaction energies and Hammett's σ parameter for various donor-acceptor combinations.
- Electron density at the bond critical point serves as a reliable indicator of halogen bond order.
Conclusions:
- Aromatic substituents significantly modulate halogen bond strength, with electron-donating groups generally enhancing the interaction.
- The position of the electron-donating group (within or outside the ring) does not fundamentally alter the substituent effect.
- Computational methods, including AIM theory, provide valuable insights into the nature and strength of halogen bonding.
Related Concept Videos
02:45Alkyl Halides
Structural Properties
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
01:16Electrophilic Aromatic Substitution: Overview
In an electrophilic aromatic substitution reaction, an electrophile substitutes for a hydrogen of an aromatic compound.
01:11ortho–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...
01:24ortho–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...
01:11Nucleophilic Aromatic Substitution: Elimination–Addition
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...
01:15Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene
Chlorination and bromination are important classes of electrophilic aromatic substitutions, where benzene reacts with chlorine or bromine in the presence of a Lewis acid catalyst to give halogenated substitution products. A Lewis acid such as aluminium chloride or ferric chloride catalyzes the chlorination, and ferric bromide catalyzes the bromination reactions. During the bromination of alkenes, bromine polarizes and becomes electrophilic. However, in the bromination of benzene, the bromine...