Abstract
On the Transmission of Substituent Effects in Fluorenes and FluorenonesA series of 2‐ and 2,7‐substituted fluorenes (1) and fluorenones (2) were prepared either by electrophilic substitution (1c–f, h–j; 2c, d, j), reduction (1, 2k, l) or nucleophilic exchange (1g, m, n; 2m) via respective diazonium compounds as well as by oxydation (2e–h, n) of the hydrocarbons (1).The carbon‐13 n.m.r. spectra for the fluorene (1a–n) and fluorenone (2a–n) derivatives was analyzed using a dual substituent parameter (DSP) equation. The substituent chemical shifts (SCS) of the carbon atoms 4a, 4b, 7 and 4a, 4b, 7, 9 of eleven fluorenes and nine fluorenones, respectively, correlate with the 𝒻, 𝓇 substituent constants and with σI, σ ones in a satisfactory manner. The comparison indicates that the correlation with the 𝒻, 𝓇 constants yields always a higher resonance contribution than the calculation with σI, σ constants. The DSP analysis reveals that transmission of the substituent effect to the substituted ring is primarily resonance controlled while the transmission to the second ring involves a π‐bond polarization mechanism. For C‐4b in the unsubstituted ring a reversed substituent effect was found. In contrast to fluorenes in fluorenones the transmission of the substituent effect involves the carbon atom 9.
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