Externally-fused cyclopenta moieties in non-alternant CP-PAHs act as peri-substituents

The Hammett constants σm for the externally fused cyclopenta moiety in the CP-PAHs 1(1,8-CP), 2(1,9-CP), 3(1,10-CP) and 4(3,5-CP) have been determined. The σm values for these structurally different CP-PAHs are nearly identical. This gives evidence that the cyclopenta moiety acts as a peri-substituent with σm=0.4±0.07.