Nbs Bromination
Nbs Bromination - Related Videos
01:27
Radical Substitution: Allylic Bromination
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2025
In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...
01:15
Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene
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2025
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...
01:15
α-Bromination of Carboxylic Acids: Hell–Volhard–Zelinski Reaction
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2023
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the Hell–Volhard–Zelinski reaction. The reaction is catalyzed by phosphorus tribromide, which can be used directly or produced in situ from red phosphorus and bromine. The mechanism comprises PBr3 catalyzed conversion of acid to acid bromide and hydrogen bromide. The acid bromide enolizes to its enol form in the presence of HBr. The nucleophilic enol attacks the bromine molecule...
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...
11:51
Construction of Defined Human Engineered Cardiac Tissues to Study Mechanisms of Cardiac Cell Therapy
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Cited by 16 •
2016
This manuscript describes the creation of defined engineered cardiac tissues using surface marker expression and cell sorting. The defined tissues can then be used in a multi-tissue bioreactor to investigate mechanisms of cardiac cell therapy in order to provide a functional, yet controlled, model system of the human heart.
FAQs
N-bromosuccinimide acts as a controlled bromine source rather than supplying a large bromine concentration at once. This maintains a low level of Br2 in the reaction mixture, allowing the radical sequence to favor allylic or benzylic C–H sites. The controlled bromine availability is therefore closely connected to the method’s useful selectivity.
A bromine radical first abstracts hydrogen from an allylic or benzylic C–H bond. That step forms a resonance-stabilized carbon radical, which then reacts with Br2 to create the C–Br bond and regenerate a bromine radical. Because the radical intermediate participates in a continuing chain process, both hydrogen abstraction and bromine transfer are central to product formation.
Resonance stabilization makes the radical formed at an allylic or benzylic position especially important in the reaction pathway. After hydrogen abstraction, the unpaired electron can be stabilized through the surrounding unsaturated or aromatic system, helping direct bromination toward those C–H bonds. This explains why the method is useful for selectively preparing allylic and benzylic bromides.
The radical pathway can be initiated with light, heat, or a peroxide initiator. These conditions generate or support the radical species needed for hydrogen abstraction and subsequent bromine transfer. Selecting one of these initiation approaches is important because the reaction depends on radical activity rather than on simple, nonradical bromine addition.
A source-supported workflow involves exposing a suitable molecule containing allylic or benzylic C–H bonds to N-bromosuccinimide, then applying a radical-promoting condition such as light, heat, or a peroxide initiator. The reaction is directed toward formation of the corresponding allylic or benzylic bromide, which can then serve as a synthetic intermediate.
The method is particularly valuable when a synthesis requires an allylic or benzylic bromide as a reactive intermediate. These products can participate in substitution, elimination, coupling, and carbon-carbon bond-forming reactions. Consequently, NBS bromination does more than install bromine: it creates a functional handle that supports several subsequent transformations in organic chemistry.