Draw the mechanism for the reaction of 3-methylbutanoic acid and oxalyl chloride to form 3-methylbutanoyl chloride. The mechanism is similar to that of the reaction of thionyl chloride (SOCl₂) with a carboxylic acid. It starts with the formation of a mixed acid anhydride intermediate. This anhydride undergoes nucleophilic acyl substitution by the chloride ion, to remove the leaving group which further breaks into carbon dioxide, carbon monoxide, and chloride ion.

• A.
• B.
• C.
• D.

Answer: (C)