The top recommend SU Chemistry department freeware for students to use when drawing chemical structures is ChemSketch - available for free for academic/educational use from ACD/Labs. A few other free options are shown in the box below, if you would like to explore some other possibilities....
Chemical Structure Drawing via Chang Bioscience - Warning! This freeware uses Java
Chem Axon - has multiple programs to choose from, depending on what you want to do
Accelrys Draw - has free versions for academic use (formerly called Symyx Draw & Isis Draw before they combined into Accelrys Draw)
