The torquoselectivity theory predicts the direction of ring-opening of
a cyclobutene substituted by electron donors and acceptors. See William
R. Dolbier, Jr., Henryk Koroniak, K. N. Houk, and Chimin Sheu, Acc. Chem.
Res., 1996, 29, 471-477.
This art illustrates some of the research of Prof. Ken Houk's group at UCLA.
Note: the images here are reduced in color depth and resolution for viewing
on the web. They are not print quality.