1. Department of Chemistry, University of Houston, Houston, TX 77204 USA;2. Department of Chemistry & Biochemistry and the Materials Science Institute, University of Oregon, Eugene, OR 97403-1253 USA
Abstract:
Whether tetra-tert-butyl-s-indacene is a symmetric D2h structure or a bond-alternating C2h structure remains a standing puzzle. Close agreement between experimental and computed proton chemical shifts based on minima structures optimized at the M06-2X, ωB97X-D, and M11 levels confirm a bond-localized C2h symmetry, which is consistent with the expected strong antiaromaticity of TtB-s-indacene.