Molecule of the Day: DEET
As the spread of West Nile Virus continues, the interest in mosquito repellent will undoubtedly skyrocket. The best known molecule to repel mosquitoes is N,N-diethyl-3-methylbenzamide or DEET. It is found in products such as "OFF".
DEET was not designed on a computer or derived from ancient folk medicine. In the 1950's, a massive screening was carried out in which all chemicals scientists could get their hands on were simply applied to volunteers' forearms, and the forearms were placed in chambers filled with hungry mosquitoes. DEET emerged as the best mosquito repellent, and has been used ever since. No one is sure why it works, it might just "smell bad" to the mosquitoes. Another known repellent is shown as well. Although the structures are similar, nobody understands the connection. Related to recent class discussions, they both have a carboxylic acid derivative, DEET contains an amide, while the other repellent has two ester groups.

Although DEET was used for decades before it was tested for safety, recent testing indicates it is safe (despite some unfounded and widely publicized claims to the contrary). Below are some good scientific articles that describe the history, activity, and relative safety of DEET

Fradin MS. Mosquitoes and mosquito repellents: a clinician's guide.
Ann Intern Med. 1998 Jun 1;128(11):931-40.

Osimitz TG, Grothaus RH. The present safety assessment of deet.
J Am Mosq Control Assoc. 1995 Jun;11(2 Pt 2):274-8.

Goodyer L, Behrens RH. Short report: The safety and toxicity of insect repellents.
Am J Trop Med Hyg. 1998 Aug;59(2):323-4.