Acyl chlorides, also known as acid chlorides, are organic compounds with the general formula RCOCl, where R is an alkyl or aryl group. They are highly reactive intermediates used extensively in organic synthesis, particularly in the formation of esters, amides, and other acyl derivatives. Their high reactivity stems from the presence of the electronegative chlorine atom, which makes the carbonyl carbon more susceptible to nucleophilic attack.