The Effects of Ring Strain on Cyclic Tetraaryl[5]cumulenes

Cyclic tetraaryl[5]cumulenes ( 1 a–f ) have been synthesized and studied as a function of increasing ring strain. The magnitude of ring strain is approximated by the extent of bending of the cumulenic core as assessed by a combination of X‐ray crystallographic analysis and DFT calculations. Trends are observed in 13 C NMR, UV‐vis, and Raman spectra associated with ring strain, but the effects are small. In particular, the experimental HOMO‐LUMO gap is not appreciably affected by bending of the [5]cumulene framework from ca. 174° ( λ max =504 nm) in 1 a to ca. 178° ( λ max =494 nm) in 1 f .