periselectivity

https://doi.org/10.1351/goldbook.P04499
The differentiation between two symmetry-allowed processes, for example the [2+4] vs. [4+6] @C01496@ of cyclopentadiene to tropone.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1150 [Terms] [Paper]