Carbon-13 chemical shifts of substituted t-butylbenzenes, phenyltrimethylsilanes and phenyltrimethylgermanes

1H,13C, and73Ge NMR spectral analysis of substituted aryltrimethylgermanes

“…Carbon-13 NMR data for substituted aryltrimethylgermanes Inc.) in anhydrous diethyl ether dried over Linde 4A molecular sieves for at least one day prior to use. Physical properties agreed with those previously reported by us 8,12 and by others. 15 -17 Purity of all compounds probably exceeds 95% as indicated by absence of spurious resonances in the 1 H and 13 C NMR spectra.…”

“…The 73 Ge spectra obtained here display an overall chemical shift range approaching 4.6 ppm, exceeding the 1.35 ppm range observed for the quaternary carbon 13 C shifts in t-butylbenzenes 12 and for 29 Si shifts (2.43 ppm) reported in aryltrimethylsilanes, 19 but somewhat less than the 119 Sn chemical shift range (4.9 ppm) recorded for aryltrimethylstannanes, 13 all systems similarly substituted. Table 3 provides parameters from least-squares regression analyses of 1 H, 13 C, and 73 Ge NMR shifts against normal Hammett sigma substituent constants.…”

“…1 H and 73 Ge chemical shifts, and 73 Ge resonance linewidths at half-height are listed in Table 2. Assignments of 13 C resonances were based on (i) additivity relationships; (ii) off-resonance protoncoupled spectra; (iii) comparison of 13 C chemical shifts with those reported in our previous studies of substituted t-butylbenzenes, 12 aryltrimethylsilanes, 12 -germanes, 12 and -stannanes; 9,10,12 and for four derivatives, and (iv) established trends in magnitude of J 19 F-13 C and J 119 Sn-13 C coupling constants in these systems. 9,10 The 73 Ge spectra in this work display relatively sharp resonances with half-height peak widths ( …”

“…20,21 This derived value determines the order: p-C CH 3 3 ( 0.197) 20,21 < p-Sn CH 3 3 ( 0.140) 11 < p-Si CH 3 3 ( 0.070) 20,21 Spectral Assignments and Reference Data < p-Ge CH 3 3 (C0.13), with the caveat that p-C CH 3 3 and pSi CH 3 3 values were determined from reactivity studies while p-Sn CH 3 3 and p-Ge CH 3 3 come from ground-state NMR work. In an attempt to facilitate a true comparison of ground-state electronic effects among these group 14 substituents, it is therefore instructive to apply the correlations in Table 4 to the literature 13 C chemical shift data for p-bis(t-butyl)benzene 12 and p-bis(trimethylsilyl)benzene 12 to produce ground-state NMR-based values for all groups. Use of regression analysis data in Table 4 and 13 C shifts of p-bis(tbutyl)benzene of C-1, CH 3 , and C-˛lead to an average sigma constant of 0.12, in remarkably good agreement with the standard reactivitybased value of 0.197 20,21 for p-C CH 3 3 .…”

Techniques for Signal Assignment in 13C‐NMR Spectroscopy of Naturally Occurring Aromatic Compounds

“…A few successful examples, however, show that complexation is often localized. For several tocopherols such as Vitamin E (18), Eu(FODh shifts the phenolic oxycarbon five times more than the ethereal one, and allows differentiation of the ortho-carbons from the ones meta to the phenol as well.I6\> In the xanthone sterigmatocystin (19), the same shift agent "complexes preferentially at the methoxy group"," while for the Rauwolfia alkaloid reserpine (20), Pr(FOD), attaches itself to the trimethoxy system in the substituted benzoic acid moiety. '''''· the latter observation is explained by the recent demonstration by 'H-NMR that Pr(FOD), associates weakly with simple anisoles, but strongly with ortho di-and tri-ethers.!"…”