Question

What is the order of rate of reaction of the following compound with phenyl magnesium bromide?

Answer 1

Grignard reagent.

• Phenyl magnesium bromide $\left({\mathrm{C}}_6{\mathrm{H}}_5\mathrm{MgBr}\right)$ is a Grignard reagent.
• Grignard reagents are organomagnesium halides having the general formula R-MgX where X can be Cl, Br, or I; R can be an alkyl, alkenyl, alkynyl, aralkyl, or aryl group or may also be an alicyclic or a heterocyclic group.

Rate of reaction of compounds with phenyl magnesium bromide.

• The IUPAC name of the given compounds are,

(I) - Acetyl chloride

(II) - Acetaldehyde

(III) - Ethyl acetate

• In the case of (I), the phenyl anion will attack the carbon atom and thus the chlorine atom cleaves the bond with carbon easily.
• The ${\mathrm{Cl}}^{-}$ion is an electron withdrawn group.
• Since it breaks the bond easily, it increases the rate of reaction due to the negative inductive effect.
• In the case of (II), when the phenyl anion attacks the carbon atom, the $\mathrm{\pi }$-electrons get shifted to the oxygen atom.
• Here, the$-\mathrm{H}$ group acts as a neutral group. Hence, it shows less rate of reaction compared to the compound (I).
• In the case of (III), when the phenyl anion attacks the carbon atom, the lone pair of electrons containing the$-\mathrm{O}$ group will form a $\mathrm{\pi }$ bond.
• Thus it decreases the rate of reaction due to the mesomeric effect.

Hence, the order of the rate of reaction of the given compounds with phenyl magnesium bromide is (I) > (II) > (III).