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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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Crystal and Molecular Structure of l-Diaz0-2,3,4,5-tetraphenylcyclopentadiene M , = 396.30, monoclinic space group P2,/c, a = 10.145(2), b = 18.523(4), c = 12.443(2) A, fi = 110.31(2)", V = 2193(1) A', Z = 4, D, = 1.201 Mg m-3, F(000) = 832, i(MoKz) = 0.71069 A, p = 0.7 mm-'. The crystal structure was determined by direct methods and refined by least-squares procedure to the discrepancy factor R = 0.039. M , = 396.30, monokline Raumgruppe P2,/c, a = 10.145(2), b = 18.523(4), c = 12.443(2) A, = 110.31(2)", V = 2193(1) A3, Z = 4, D, = 1.201 Mgm-3, F(000) = 832, i.(MoKz) = 0.71069 A, p = 0.7 mm-'. Die Kristallstruktur wurde mit direkten Methoden gelost und nach der Methode der kleinstcn Quadrate bis zu einem R-Wert von 0.039 verfeinert.

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