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  4. The order of reactivities of methyl halide in the formation of Grignard reagent is

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Q. The order of reactivities of methyl halide in the formation of Grignard reagent is

AMUAMU 2005

Solution:

When an alkyl halide reacts with $Mg$ metal in dry ether, as a solvent, in an atmosphere of nitrogen then alkyl magnesium halide is obtained. This is called Grignard reagent.
$ RX+Mg\xrightarrow{\text{Dry ether}}R-Mg-X $
The reactivity with respect to halide
$ RI > RBr > RCl $
For a given halide the order is
Allyl > alkyl $(3^{\circ} > 2^{\circ} > 1^{\circ} ) > $ aryl.
The order of reactivity of methyl halide in the formation of Grignard reagent is as
$ CH_{3}I > CH_{3} Br > CH_{3}Cl $
Here the alkyl group is same, therefore the reactivity depend on halides. The ease of the leaving group in alkyl halide is as
$ -I > -Br > -Cl -F $
and the bond strength being in order
$C - F > C - Cl > C - Br > C - I$.
Therefore, the reactivity of methyl halide in the formation of Grignard reagent is as
$ CH_{3}I > CH_{3}Br > CH_{3}Cl $