What happens when NBS is added to alkene?

Alkenes react with NBS in dry CCl4 under reflux conditions to give allyl bromide. The reaction is initiated by light or peroxide. Although a number of reagents are available for bromination of allylic C-H bond of alkenes, NBS is most commonly used. The reaction is called Wohl-Zigler bromination.

What is the purpose of NBS?

N-Bromosuccinimide (NBS) is a brominating and oxidizing agent that is used as source for bromine in radical reactions (for example: allylic brominations) and various electrophilic additions.

Is NBS a strong base?

NBS, in the presence of a strong base, such as DBU, reacts with primary amides to produce a carbamate via the Hofmann rearrangement.

Which is the reagent for allylic bromination [ NBS ]?

Allylic Bromination Explained: Under radical conditions, alkanes containing allylic hydrogens enter into allylic halogenation. A particularly good reagent for allylic bromination is N -bromosuccinimide (NBS). The bromine reacts with the alkene by radical chain mechanism.

How are benzylic hydrogens similar to allylic hydrogens?

Predict the product of the allylic bromination reaction of 2-benzylheptane. (Hint: How are benzylic hydrogens similar to allylic hydrogens?) The reactant 5-isopropyl-1-hexene generates the products 3-bromo-5-isopropyl-1-hexene and 1-bromo-5-isopropyl-2-hexene.

When to use N-bromosuccinimide ( NBS ) or hν?

When treated with N-bromosuccinimide (NBS) and light ( hν ) alkyl groups adjacent to the alkenes will be converted into alkyl bromides. Under radical conditions, alkanes containing allylic hydrogens enter into allylic halogenation.

Why are alkyl halides prepared at the allylic position?

A radical intermediate is generated, which is stabilized by resonance. The stability provided by delocalization of the radical in the alkene intermediate is the reason that substitution at the allylic position is favored over competing reactions such as addition at the double bond.