Acyl chlorides are compounds containing the functional group.
They occur naturally in onions, and as do onions, they cause the eyes to run and sting. This is because they react with moisture in the eyes to form carboxylic and hydrochloric acids. The polar nature of the carbonyl group makes them very reactive. They react vigorously or even explosively with nucleophiles such as water, alcohols, ammonia, amines, and hydroxide ions. The main products are shown below.