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 C-13 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 degrees (lambda(max)=504 nm) in 1 a to ca. 178 degrees (lambda(max)=494 nm) in 1 f.

Automated summary

Cyclic tetraaryl[5]cumulenes were synthesized and studied to understand the effects of increasing ring strain. Analysis through X-ray crystallography and DFT calculations showed that while there were observable trends in C-13 NMR, UV-vis, and Raman spectra associated with ring strain, the HOMO-LUMO gap was not significantly affected by the bending of the [5]cumulene framework.