13C‐ and1H‐NMR‐spectroscopical Investigations of 2,9‐substituted FluorenesThe13C‐ and1H‐chemical shifts for a series of 9‐substituted fluorenes and 9‐substituted 2‐nitrofluorenes, where the substituents are various azarenium ions, have been determined, shift data for several other fluorenyl compounds are also presented. The exact assignments of the13C‐signals are possible by comparison of calculated shifts from13C‐data with experimental1H‐values. The substituent effects are discussed in terms of transmissions of electronic interactions. The substituent chemical shifts (SCS) for selective positions of the fluorene system give a linear correlation with the substituent constants σI,F, respectively. An increment model for the calculation of the empirical13C‐chemical shifts of N‐(2‐nitrofluorene‐9‐