3 Ways to Form Carbon Carbon Bonds
Introduction
A significant factor of organic chemistry is synthesis: starting with one compound and using reagents to convert the starting material to an end product. While a large component of synthesis is understanding how to convert one functional group to another, being able to create new carbon carbon bonds is also useful to know.
Using Cyanide as a Reagent
Cyanide (carbon triple-bonded to nitrogen) can be used to add C-C bonds to a molecule. Cyanide is a good choice of reagent for adding C-C bonds to aldehydes and ketones. However, with carboxylic acids, cyanide will create an acid-base reaction. Cyanide also won't react much with esters or amides.
Reaction Mechanism of Cyanide and a Ketone
First the negatively charged carbon in cyanide attacks the carbonyl carbon in the ketone. This breaks the double bond in the carbonyl, resulting in a tetrahedral intermediate with two methyl groups and a negatively charged oxygen (from the previous formed ketone) and a cyanide molecule.
By doing a H+ workup, the negatively charged oxygen gains a H, forming an alcohol. The molecule is now a cyanohydrin: it has a cyano group (CN) and a hydroxl group (OH) attached to the same carbon atom.
Using Grignards as a Reagent
Grignard reagents are strong nucleophiles that can also be used to make carbon-carbon bonds.
If there is an acidic proton present, grigards will do an acid-base reaction, instead of creating a carbon-carbon bond, since acid-base reactions are virtually one of the fastest types of reactions. While a grignard is a good choice for an aldehyde or ketone, it is not a good reagent to make carbon-carbon bonds in a carboxylic acid.
Grignards and a carboxylic acid will only undergo an acid-base reaction.
Using Organolithium as a Reagents
Organolithium is made by reacting a carbon chain with a halogen connected to a carbon on one of the ends with lithium metal. This reaction creates a carbon chain with a lithium attached, LiH, and water.
While organolithium reagents can do virtually the same reagents with carbonyl compounds as Grignard reactions do, organolithium reagents create stronger bases than Grignard reagents. In addition, organolithium reacts violently with air and water.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2020 Christina Garvis
