Question: Identify the reagents represented by the letters a–e in the following scheme:

It is defined as the substance or the compound added in the chemical reaction to complete the reaction and the formation of the desired product occurs for every reaction specific reagent is used as per the product formation.

As we see that the benzene is showing acylation by the addition of the COCH₃CH₂ and for acylation the reagent used is CH₃CH₂COCl,AlCl₃.

As the reduction of the carbonyl is occurring and conversation of the acylated benzene to the alkylbenzene and the reduction of the carbonyl is done by the Lindlar’s catalyst which is H₂/Pd, C.

Bromination is done when the addition of the bromide ion is done at the para position and the reagent used for the bromination is Br₂,PBr₃ added Br ion to the molecule.

Now, the bromination is done at the alkyl chain attached to the benzene ring here the reagent used is the N- bromo succinimide (NBS) which provides the BR ion which directly acts as an electrophile but cannot do bromination at benzene ring because bromination at benzene is only possible by the presence of the Br ion with PBr₃ or FeBr₃ so, bromination occurs at alkyl group in presence of NBS only.

Here, elimination is occurring when the removal of the halide ion occurs and the formation of alkene occurs this is done by the abstraction of proton in the presence of base which abstracts the proton then followed by halide ion removal. Alkene formation takes place and the base reagent which is used is KOH, ethanol