Why are perfluorocyclobutadiene and some other (CF)(n)(q) rings non-planar?
Although surprising, the nonplanarity of C(2h) C(4)F(4) is not unique. While C(6)F(6) is planar, other members of the (CF)(n) family, for example, C(5)F(5)(-), C(6)F(6)(-), C(7)F(7)(-), and triplet C(7)F(7)(-) are not. C(2h) C(4)F(4) is not aromatic, as claimed (see above), but its antiaromaticity is reduced relative to the planar D(2h) form due to decreased pi antibonding and enhanced cross-ring pi overlap. The nonplanar C(2h) geometry also benefits from the relief of repulsive FC-CF bond eclipsing interactions.
Wu
Judy I
JI
Center for Computational Chemistry, Department of Chemistry, University of Georgia, Athens, Georgia 30602-2525, USA.
Evangelista
Francesco A
FA
Schleyer
Paul von Ragué
Pv