The structure of phenylcyclopropane radical cation (1(.+), R = H) is derived from CIDNP effects observed during the electron transfer reaction of 1 with chloranil. This species is an example of an elusive structure type. The secondary cyclopropane protons show significantly divergent hyperfine coupling constants due to an unprecedented stereoelectronic effect. Incorporation into a redox-active pentasil zeolite (Na-ZSM-5) converts 1 or its p-methoxy derivative (1, R = OCH3) to trans-propenylarene radical cations (2(.+), R = H, OCH3).