Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : II. ( 119Sn- 13C) coupling constants and 13C chemical shifts of meta- and para-derivatives

Abstract

Carbon-13 NMR data are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, RC 6H 4Sn(CH 3) 3, where R = para-N(CH 3) 2, para-OCH 3, para-OC 2H 5, para-CH 3, meta-CH 3, -H, para-F, meta-OCH 3, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH 3) 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, C 1 and C 4 carbons, and with the carbon-13 chemical shifts δ(C(1)). In the meta-derivatives, the couplings | J(Sn-CH 3)|:, |: 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) > CH 3 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) > CH 3. The magnitudes of the tin coupling constants decrease C(1) > CH 3 > C(3, 5) > C(2, 6) > C(4) in the para-derivatives, while in the meta-series the order is C(1) > CH 3 > C(3), C(5) > C(2) > C(6) > C(4). The two sets of one-bond |: J(Sn-CH 3)|: 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.