Since Grignard reagents are powerful nucleophiles, we cannot prepare a Grignard reagent from any organic halide that contains a carbonyl, epoxy, nitro, or cyano $(- CN)$ group. If we were to attempt to carry out this kind of reaction, any Grignard reagent that formed would only react with the unreacted starting material
This means that when we prepare Grignard reagents, we are effectively limited to alkyl halides or to analogous organic halides containing carbon - carbon double bonds, internal triple bonds, ether linkages, and -$NR_2$ groups

$\left( C _6 H _5\right)_3 C - Cl \frac{ OH ^{-}}{\text {Pyridine }}\left( C _6 H _5\right)_3 C - OH$

