Reaction of Grignard Reagents: Alkenes, Alkynes, Alcohols, Alkanes, Amines

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SUMMARY

Grignard reagents react primarily with functional groups that possess acidic protons, specifically terminal alkynes, alcohols, and secondary amines. Alkenes, nonterminal alkynes, alkanes, and tertiary amines do not react due to their lack of acidic protons and poor leaving group ability. The reaction mechanism involves acid-base interactions, resulting in the formation of magnesium acetylides, alkoxides, and amides. Importantly, Grignard reagents cannot be formed in the presence of alcohols due to their decomposition into hydrocarbons and magnesium salts.

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Soaring Crane
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1. Which of the following functional groups react with Grignard reagents: alkenes; terminal alkynes; nonterminal alkynes; alcohols; alkanes; tertiary amines; secondary amines?

I know Grignard reagents react with electrophiles. This would include alcohols, secondary and tertiary amines?

2. You can form a Grignard in the presence of an alcohol. Explain your answer.

This is false because alcohol has an -OH group. The Grignard reagent would decompose since the products that would follow would be a hydrocarbon R-CH and a Mg salt, HO-Mg-Br.

Thank you.
 
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Soaring Crane said:
1. Which of the following functional groups react with Grignard reagents: alkenes; terminal alkynes; nonterminal alkynes; alcohols; alkanes; tertiary amines; secondary amines?

I know Grignard reagents react with electrophiles. This would include alcohols, secondary and tertiary amines?
The important consideration for all of these compounds is that 1) none of the functional groups mentioned are good leaving groups, and 2) Grignard reagents are extremely strong bases. This means that the only reactions you're going to expect out of any of these functional groups are acid-base reactions. So then you have to determine which of the listed functional groups have acidic protons. Alkenes and alkanes (without some activating group) are both out, and tertiary amines don't have any protons to give on the nitrogen center. Ditto for nonterminal alkynes. That leaves terminal alkynes, alcohols, and secondary amines, all of which have acidic protons that can react with Grignard reagents. The products of these reactions are magnesium acetylides, alkoxides, and amides, respectively.
 

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