“…[60] Symmetric aromatic CC stretch vibrational modes in the 1568 ± 1628 cm À1 region were previously found to correlate with the degree of iminocyclohexadienyl character of several arylnitrenium ions. [48,56,60] Comparison of similar modes in 2-fluorenylnitrene indicates this kind of correlation for arylnitrene species is not as clear and appears to be complicated by the nature of the nitrene moiety. For example, the singlet and triplet 2-fluorenylnitrenes have very similar vibrational frequencies of the CC stretch mode (1575, 1579, and 1604 cm À1 for the singlet state and 1577, 1578, and 1605 cm À1 for the triplet state) although the aromatic C À C and CÀN bonds are noticeably different in the optimized geometries shown in Figure 3.…”