Carbon-Carbon bond formation

​​In a nutshell

Carbon-carbon bond synthesis is used to lengthen the carbon chain. Reagents which have a nucleophilic or electrophilic carbon atom are used to form a new carbon-carbon bond.

Equations

These are general chemical equations. You will need to be able to use these when you write equations for specific substances.

$$haloalkane \ + \ cyanide \xrightarrow[ethanol]{reflux} nitrile \ + \ salt \\ \ \\carbonyl \ + \ cyanide \rightarrow hydroxynitrile$$​​

Cyanides

​Cyanides are nucleophiles which can attack an electron deficient carbon atom. 

Nucleophilic substitution 

A nitrile can be produced by reacting cyanide in ethanol with a haloalkane via a nucleophilic substitution reaction. This is because the halogen is more electronegative than the carbon, giving rise to a polar bond and a partially positive carbon atom.

​$$haloalkane \ + \ cyanide \xrightarrow[ethanol]{reflux} nitrile \ + \ salt$$​​

Example

​$$chloromethane \ + \ potassium \ cyanide \xrightarrow[ethanol]{reflux} acetonitrile \ + \ potassium \ chloride \\ \ \\CH_3Cl \ + \ KCN \xrightarrow[ethanol]{reflux} CH_3CN \ + K^+Cl^-$$​​

Nucleophilic addition

Hydroxynitriles (cyanohydrins) can be produced by reacting acidified cyanide with a carbonyl compound. The cyanide acts as a nucleophile and attacks the partially positive carbon and adds itself to the molecule. 

​$$carbonyl \ + \ cyanide \rightarrow hydroxynitrile$$​​

Example

​$$propanone \ + \ sodium \ cyanide \xrightarrow{H^+} 2-hydroxy-2-methylpropanenitrile \\ \ \\C_3H_6O \ + \ NaCN \xrightarrow{H^+}C_3H_6OHCN \\ \ \\Structural \ formula \ of \ the \ product: \ CH_3CHCH_3(OH)CN$$​​

General Mechanism

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Risk assessment

Potassium cyanide is an irritant. It can react with moisture to produce hydrogen cyanide (toxic gas). To reduce risks when working with potassium cyanide, perform the experiment in a fume cupboard.  

Important: Always wear safety goggles, a lab coat and gloves when carrying out a chemistry experiment. 

Friedel-Crafts reactions

Friedel-Crafts reactions can be used to make new carbon-carbon bonds with benzene. Friedel-Crafts alkylation adds an alkyl group to the benzene ring. Friedel-Crafts acylation adds an acyl group to the benzene ring.