Figure shows each bond length of 1 + ,2 + in 1 + TfO -,2 + TfO -. Compared to that of the reported triarylpropargyl alcohols, there is a slight change in bond lengths, with elongation of C2≡C3 bond and contraction of C3-C4 bond, thus crystallographically demonstrating the reduced bond alternation in triarylpropargyl cations. This is consistent with a low wavenumber shift of the C≡C stretching vibration. These results revealed that , in alkynyl carbocations, the delocalized nature of the electronic structure is a more significant characteristic than the degree of bond-length alternation as determined experimentally via spectroscopic and crystallographic measurements.