AbstractThe17O NMR chemical shift data for 23 9‐fluorenones in acetonitrile at 75°C are reported.17O NMR data for the 3‐substituted 9‐fluorenones are correlated with17O NMR data for 4‐substituted acetophenones. Chemical shift data for 1‐halogeno‐9‐fluorenones are deshielded relative to the 3‐isomers, suggesting important repulsive van der Waals interactions. The keto carbonyl signal for 9‐fluorenone‐1‐carboxylic acid is substantially shielded, as expected, from intramolecular hydrogen bonding. The data for several multi‐substituted 9‐fluorenones demonstrate that substituent effects are addi