Scanning tunneling microscopy (STM) was used to investigate the reaction of 1,3-cyclohexadiene with Si dimers on the bare Si(100) surface. Detailed, high-resolution STM images show a distribution of surface products. In addition to the intradimer [2 + 2] and [4 + 2] reaction products previously reported, two different [2 + 2] conformers are identified. Empty state STM images also show interdimer [4 + 2] reactions involving neighboring dimers in the same row and in adjacent rows. The former are shown to be the dominant surface product despite the presence of unpaired dangling bonds on two adjacent dimers. These results are interpreted in terms of a reaction mechanism in which the reduced ring strain favors the kinetic interdimer [4 + 2] product over the thermodynamically stable [4 + 2] intradimer product.