OP needs to clarify if they mean one engine in the middle of the vertical stabilizer (e.g. Lockheed L-1011), or two engines at the tail of the aircraft (e.g. MD-80). Though some have both (e.g. Boeing 727).

If you want an odd number of engines on aircraft, one of the engines need to be in the middle of the aircraft. So the middle of the vertical stabilizer is a good place. This design made sense back when 2-engine airliners were not allowed to fly overseas routes, but 4 engines became expensive, so they opted for 3 engines. More recently, some small jets have a single engine, and at least one design (PiperJet) was developed with an engine in the vertical stabilizer.