Measuring antiaromaticity by an analysis of ring current and coupling constant changes in a cyclopentadienone-fused dihydropyrene.
The synthesis of the chloro- and parent cyclopentadienone-fused dihydropyrenes 10 and 7 are reported. Analysis of coupling constants, and chemical shift changes between these and the nonconjugated dihydro derivatives 11 and 8, and between the benzannulene 4 and the parent annulene 12, indicates without doubt that cyclopentadienone is behaving as an antiaromatic 4n-pi system and that in its effect on the ring current of 12, cyclopentanedienone has about 80% of the effect of benzene. This is the first time that a suitable probe has been used to estimate the relative ability of a 4n-pi system to bond localize the probe in comparison to the (4n + 2)-pi system benzene.
Mitchell
Reginald H
RH
Department of Chemistry, University of Victoria, Post Office Box 3065, Victoria, British Columbia, Canada V8W 3V6. regmitch@uvic.ca
Zhang
Rui
R
Fan
Wei
W
Berg
David J
DJ