Related Experiment Video
Updated: May 20, 2026
06:44
From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Unexpected trends in halogen-bond based noncovalent adducts
Stefan M Huber1, Elisa Jimenez-Izal, Jesus M Ugalde
1Department Chemie, Technische Universität München, Lichtenbergstraße 4, D-85747 Garching, Germany. stefan.m.huber@tum.de
Chemical Communications (Cambridge, England)
|June 30, 2012
Summary
Halogen bond strength is not always increased by more electronegative groups. This study reveals unexpected trends in Lewis acidity for halogen-bond donors, challenging common assumptions in chemistry.
Area of Science:
- Chemistry
- Supramolecular Chemistry
- Chemical Bonding
Background:
- Halogen bonding is a non-covalent interaction involving a halogen atom acting as a Lewis acid.
- The strength of halogen bonds is typically correlated with the electron-withdrawing ability of the group attached to the halogen atom.
- Understanding factors influencing halogen bond strength is crucial for designing novel materials and catalysts.
Purpose of the Study:
- To investigate the relationship between the electronegativity of the R group in R-X compounds and the strength of the resulting halogen bond.
- To explore unexpected trends in halogen-bond donor strength using CY3I (Y = F, Cl, Br, I) as model systems.
- To challenge the conventional understanding of Lewis acidity in halogen-bond donors.
Main Methods:
- Synthesis and characterization of halogen-bond adducts.
- Experimental determination of halogen bond strengths using techniques such as X-ray crystallography and spectroscopy.
- Computational modeling to support experimental observations and elucidate electronic effects.
Main Results:
- Observed unexpected trends in halogen bond strengths for CY3I adducts with chloride and trimethylamine.
- Demonstrated that increasing the electronegativity of the Y group in CY3I does not consistently increase halogen-bond donor strength.
- Identified specific electronic effects that deviate from the expected correlation between R-group electronegativity and Lewis acidity.
Conclusions:
- The strength of a halogen bond is not solely determined by the electronegativity of the attached group.
- Factors beyond simple electronegativity play a significant role in modulating halogen-bond donor strength.
- These findings necessitate a re-evaluation of predictive models for halogen bonding and Lewis acidity.
More Related Videos
Related Concept Videos
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
03:01Halogens
Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. Astatine is a highly unstable radioactive element, so currently, most of its properties are unknown due to its short half-life. Tennessine is a synthetic element also predicted to be in this group.
02:46Halogenation of Alkenes
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
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...
01:14Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.