Question

Which of the following Grignard reagent can be prepared?

• A. $Br-Mg-{CH}_2-{CH}_2-{CH}_{2}O-H$
• B. $Br-Mg-{CH}_2-{CH}_2-SH$
• C. $BrMg-{CH}_2-{CH}_2-{NH}_2$
• D. $BrMg-C{H}_2-C{H}_2-\underset{C{H}_3}{\underset{|}{N}-}C{H}_3$

Answer 1

The correct option is D $BrMg-C{H}_2-C{H}_2-\underset{C{H}_3}{\underset{|}{N}-}C{H}_3$

Grignards reagent form via the reaction of an alkyl or aryl halide with magnesium metal.The reaction is conducted by adding the organic halide to a suspension of magnesium in an ethyal solugnt,which produce the reaction proceeds through a single electron transfer as:

$R-X+mg⟶R-X^{-}+M{g}^{+}$

$R-X^{-}⟶R+X^{-}$

$R+M{g}^{+}⟶RM{g}^{+}$

$RM{g}^{+}+X^{-}⟶RMgX$

Thus,by the above way of preparing grignard reagent,compounds with carbonyl group $(C=O)$,$-SH$ group and $-N{H}_2$ group cannot be prepared .