Wize University Organic Chemistry Textbook > Aldehydes and Ketones (Addition to Carbonyls/Reactivity of Enolates)
Reactions with Carbon Nucleophiles
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The Grignard Reaction
The Grignard reaction forms a new carbon-carbon bond.
- It requires a carbon nucleophile (called a Grignard reagent).
- The nucleophile is synthesized from an alkyl halide and magnesium.
- The reaction needs to be done in a non-protic solvent (usually diethyl ether).
- The work-up step is the addition of an acid to get rid of the negative charges.
Watch Out!
This reaction cannot be done in the presence of OH and NH bonds.
The carbon nucleophile is also a good base and will react with the OH and NH in an acid/base reaction before it behave as a nucleophile.
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Cyanohydrin Formation
A cyanohydrin has an -OH group and a -CN group bonded to the carbon of interest.
- A cyano (CN-) group is the carbon nucleophile.
- The oxygen from the carbonyl is protonated by HCN to give the final product.
- The cyano group can further react with LiAlH4 (a reducing agent) to make an amine and with acid to make a carboxylic acid.
Wize Tip
This is a reaction of lesser importance (especially when compared with some of the others in this section), but is still important to know. Knowing the reagents for the reduction of the -CN group into a primary amine (LiAlH4) and the oxidation of the -CN group into a carboxylic acid (acid/water) is also important.
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Example: The Grignard Reaction
You attempt the reaction below in the lab but instead of the desired Grignard product, you isolate starting material and a by-product. Why does the reaction fail and what is the by-product?
Remember, MeMgBr is a strong nucleophile but also a strong base (you can think of it as Me- and +MgBr). The aromatic alcohol (phenol) is mildly acidic (pKa ~ 10). In the presence of one equivalent of MeMgBr, this OH will just be deprotonated.
The by-product is methane (CH4).
Mark Yourself Question
- Grab a piece of paper and try this problem yourself.
- When you're done, check the "I have answered this question" box below.
- View the solution and report whether you got it right or wrong.
Predict the product(s) of the following reactions.
