Radical Halogenation
Radical Halogenation - Related Videos
01:34
Radical Halogenation: Thermodynamics
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2023
The thermodynamic favorability of a reaction is determined by the change in Gibbs free energy (ΔG). ΔG has two components- enthalpy (ΔH) and entropy (ΔS). The entropy component is negligible for alkane halogenation because the number of reactants and product molecules are equal. In this case, the ΔG is governed only by the enthalpy component. The most crucial factor that determines ΔH is the strength of the bonds. ΔH can be determined by comparing the energy between bonds broken and bonds...
01:33
Radical Halogenation: Stereochemistry
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2023
Stereochemistry is the study of the different spatial arrangements of atoms in a given molecule. The stereochemistry of radical halogenations can be understood from three different situations: Halogenation to form a new chiral center: For example, radical halogenation of butane forms the products 2-chlorobutane and 1-chlorobutane, where the former has a chiral center. However, 2-chlorobutane is obtained as a racemic mixture due to the trigonal planar structure of the formed radical...
03:01
Halogens
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2020
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. The halogens are not found as single atoms but exist as diatomic molecules. The atomic radius increases from fluorine to iodine. The valence shell...
01:27
Radical Substitution: Halogenation of Alkanes and Alkyl Substituents
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2023
In the presence of heat or light, alkanes react with molecular halogens to form alkyl halides by a substitution reaction called radical halogenation. This reaction has three steps: initiation, propagation, and termination, as seen in the radical chlorination of methane to produce methyl chloride. In the initiation step of the reaction, the chlorine molecule undergoes homolytic cleavage in the presence of light or heat, forming two highly reactive chlorine radicals. Propagation occurs in two...
14:22
Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
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Cited by 9 •
2013
Radical-based biomimetic chemistry has been applied to building-up libraries necessary for biomarker development.
FAQs
Initiation creates radicals from halogen molecules by homolytic cleavage under light or heat. During propagation, a halogen radical abstracts hydrogen, leaving a carbon radical that reacts with another halogen molecule. This repeats the chain sequence, while termination stops propagation by removing reactive radical intermediates. The balance between these stages determines whether substitution proceeds efficiently.
Chlorine and bromine differ in selectivity because their radical reactions respond differently to reaction conditions and carbon-radical stability. Chlorination can produce a broader product distribution, whereas bromination can show greater selectivity for pathways associated with more stable carbon radicals. This distinction affects product mixtures and helps determine which halogen is more synthetically useful.
Carbon-radical stability helps explain why halogenation does not necessarily occur equally at every available carbon-hydrogen site. A pathway that forms a more stable carbon radical can favor substitution at that position, changing the relative amounts of products. This principle connects microscopic radical intermediates with the observed selectivity and product distribution of the reaction.
Light or heat supplies the condition needed to cleave the halogen molecule homolytically and generate the radicals that begin the chain. In practice, the organic substrate and halogen are exposed to one of these activating conditions, then the resulting substitution is evaluated through its products. Changing the activation condition can therefore influence product distribution and selectivity.
Product distribution provides evidence about selectivity and the relative favorability of competing substitution pathways. Comparing the amounts or range of alkyl halides formed can show whether conditions favor a particular carbon site or generate a broader mixture. In chemistry experiments, this outcome helps assess how the chosen halogen and reaction conditions affect synthetic usefulness.
The value of alkyl halides lies in their ability to serve as starting materials for subsequent substitution, elimination, and coupling reactions. Radical halogenation therefore converts hydrocarbon structures into compounds that can undergo further chemical transformations. In synthetic chemistry, the initial product distribution matters because it influences which downstream structures can be prepared and how selectively they are obtained.