Complex Organic Molecules
In astronomy, complex organic molecules are defined as molecules with several carbon atoms such as benzene or acetic acid. These molecules have been detected in interstellar space using radio telescopes. A gas mixture of methane and nitrogen, for example, yields complex organic compounds upon UV irradiation or exposure to an electric discharge. These are sometimes referred to as tholins, and they can be formed abiotically in the atmosphere of Titan (the largest satellite of Saturn).
In chemistry, “complex organic molecules” generally refer to much larger polymer-like molecules such as proteins. Proteins are typical complex organic polymers, with well-defined three-dimensional structures, composed of 20 different amino acids. Given the immense possible variety of these polymers, they are indeed “complex.”