Answer to Question #253849 in Organic Chemistry for manjeshni

Question

Consider the reaction between toluene and isobutyl chloride

i) The first step is the reaction between the alkyl halide and AlCl3, which generates a carbocation. Show how this carbocation is formed.

ii) The carbocation generated in part (i) undergoes a transformation. Explain this transformation and give the structure of the new carbocation formed. ​

iii) Write the mechanism for the reaction that takes place between the generated

carbocation and toluene.

iv) Identify the major product and explain why this product would be formed in higher yield.

Answer 1

(1)The function of AlCl3in Friedel-Craft reaction, is to produce electrophile, which later adds to benzene nucleus. This electrophilic aromatic substitution allows the synthesis of monoacylated products from the reaction between arenes and acyl chlorides or anhydrides. The products are deactivated and do not undergo a second substitution. Normally, a stoichiometric amount of the Lewis acid catalyst is required for both the substrate and the product form complexes.AlCl3​ (and other Lewis acids like it) will coordinate to halogens, and facilitate the breaking of these bonds. In doing so, it increases the electrophilicity of its binding partner, making it much more reactive.

(2)

Whenever a nucleophile attacks some molecules, we typically see two products. However, in most cases, we normally see both a major product and a minor product. The major product is typically the rearranged product that is more substituted (aka more stable). The minor product, in contract, is typically the normal product that is less substituted (aka less stable).

The reaction: We see that the formed carbocations can undergo rearrangements called hydride shift. This means that the two electron hydrogen from the unimolecular substitution moves over to the neighboring carbon. We see the phenomenon of hydride shift typically with the reaction of an alcohol and hydrogen halides, which include HBr, HCl, and HI. HF is typically not used because of its instability and its fast reactivity rate. Below is an example of a reaction between an alcohol and hydrogen chloride: