Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : II. (119Sn-13C) coupling constants and 13C chemical shifts of meta- and para-derivatives |
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| Authors: | C.D. Schaeffer J.J. Zuckerman |
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| Affiliation: | Department of Chemistry, State University of New York at Albany, Albany, New York 12222 U.S.A. |
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| Abstract: | Carbon-13 NMR data are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, RC6H4Sn(CH3)3, where R = 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. In the para-derivatives, correlation coefficients with Hammet σ-constants of greater than ca. 0.9 are obtained with the tin-carbon couplings to methyl, C1 and C4 carbons, and with the carbon-13 chemical shifts δ(C(1)). In the meta-derivatives, the couplings |J(Sn-CH3)|:, |:J(Sn-C(1))|:, |:J(Sn-C(3))|: and |:J(Sn-C(6))|:, and the shifts δ(C(1)) and δ(C(5)) correlate well with Hammett σ. In the para-derivatives, sensitivity to change in substituent falls off C(4) > C(3, 5) > C(1) > C(2, 6) > CH3 as registered by the δ(C), while in the meta-derivatives δ(C) changes decrease C(3) > C(2), C(4) > C(1) > C(5), C(6) > CH3. The magnitudes of the tin coupling constants decrease C(1) > CH3 > C(3, 5) > C(2, 6) > C(4) in the para-derivatives, while in the meta-series the order is C(1) > CH3 > C(3), C(5) > C(2) > C(6) > C(4). The two sets of one-bond |:J(Sn-CH3)|: and |:J(Sn-C(1)|: values correspond closely to the 0.25/0.33 ratio of coefficients in the LCAO approach, and are interpreted in terms of s-electron redistributions at the tin atom with change in substituent. |
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