Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : III. Proton data at 100 MHz and the derived Hammett σ-constant of the trimethyltin group |
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Authors: | CD Schaeffer JJ Zuckerman |
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Institution: | Department of Chemistry, State University of New York at Albany, Albany,New York 12222 U.S.A. |
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Abstract: | Proton NMR data at 100 MHz are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, XC6H4Sn(CH3)3, where X = para-N(CH3)2, para-OCH3, para-OC2H5, para-CH3, meta-CH3, -H, para-F, meta-OCH3, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH3)3. Correlation coefficients with Hammett σ-constants of greater than 0.95 are obtained with the methyltin proton chemical shifts and coupling constants to carbon 1J(13C1H)] and tin 2J(SnC1H)]. Solvent effects and other extraneous factors invalidate comparisons of ? values in terms of the relative attenuation of the transmission of substituent effects through homologous carbon, silicon, germanium and tin systems, but coupling constant data reflect a diminution of ca. one tenthfold per bond in the order ?C(1)Sn] > ? SnC] > ? CH]. Satisfactory correlations (r > 0.95) are obtained in this series of closely-related compounds among the conventionally recorded two-bond, 2J(SnC1H) and the constituent, one-bond 1J (Sn13C) and J(13C1H) coupling constants, but the correlation coefficient for the comparison between the two one-bond couplings, 1J(Sn13C) and 1J(13C1H) is lower (r = 0.872). Changes in the couplings at the methyltin carbon bond tin-119 atoms are interpreted in terms of isovalent hybridization; a model based upon effective nuclear charges is tested with respect to both NMR coupling constants and 119Sn Mössbauer Isomer shifts at tin and is invalidated. Proton and carbon-13 NMR, chemical shift and coupling constant data are used to derive a Hammett σ-constant for the para-trimethyltin group of ?0.14, and the significance of this value is discussed. |
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