Many of the questions in this chapter were submitted by undergraduate students from around the country. We’ve listed all of their names in the Acknowledgement section at the beginning of the book. We want to thank them again for submitting such interesting questions, and if you have questions about chemistry that you’d like to see answered, please send them to us!

Viagra^® (Sildenafil) interferes with an enzyme located in the erectile tissue that breaks down a molecule called cGMP (cyclic gunaosine monophosphate). Viagra® slows down this enzyme, allowing the amount of cGMP to build up. cGMP is responsible for a process known as vasodilation, or widening of the blood vessels in smooth muscle cells. More blood in these vessels means a stronger erection.