Complex sentence: Cyclobutadiene is the smallest ("n")-annulene ((4)-annulene), an extremely unstable (lifetime under 5 seconds in the free state) hydrocarbon with chemical formula and a rectangular structure (with a square form hypothetically possible).
Split into simpler sentences: Cyclobutadiene is the smallest ("n")-annulene ((4)-annulene), an extremely unstable hydrocarbon having a lifetime shorter than five seconds in the free state. It has chemical formula and a rectangular structure (with a square form hypothetically possible).