The reaction of an alkyl halide with potassium cyanide is synthetically useful because it

  • A. shortens the carbon chain by one atom
  • B. produces an alkene
  • C. lengthens the carbon chain by one carbon atom
  • D. removes the halogen without adding anything

Explanation

The cyanide ion substitutes for the halogen, so the nitrile formed has one more carbon than the starting halide, and that nitrile can then be hydrolysed to a carboxylic acid or reduced to an amine. Building the chain one carbon at a time is a standard strategy in organic synthesis. Alcoholic conditions are used to favour substitution over elimination.

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