⁷³Ge and ¹³C NMR spectra of some methylgermacyclohexanes

Abstract

RESULTS AND DISCUSSION73Ge is an esoteric nucleus as far as NMR spectroscopy is concerned, chiefly because of its large quadrupolar moment, which tends to cause excessive broadening of signals, and there are many fewer reported data than for other Group IVB elements.' So

Absorption, electrochemical, theoretical, and 73Ge NMR spectral characterization of the germanium neo-pentane analogue (Me3Ge)4Ge

“…The 73 Ge NMR resonances (3), including those involved in the highest intensity absorption peak (HOMO and LUMOþ4). for 1,1-dimethyl-1-germacyclochexane, 1-methyl-germacyclohexane, and the germanium-unsubstituted germacyclohexane were observed at d À13.7, À65.3, and À131.2 ppm (respectively) [19].…”

G73e Nuclear Magnetic Resonance Spectroscopy of Germanium Compounds

“…Takeuchi et al published a series of thirteen papers in the 1980s that focused on the 73 Ge NMR of numerous germanes and correlated their spectral data with those of the analogous silicon and tin compounds [48][49][50][60][61][62][63][64][65][66][67][68][69]. Molecular mechanics calculations were also used to further explain the experimental data.…”

“…The spectrum of the unsymmetrical compound Me 3 GeCH 2 CH 2 COOH was also acquired, and this compound exhibited a resonance at δ 6.3 ppm with a ν 1/2 value of 54 Hz, where the line broadening is result of the perturbation of the electric field gradient at the germanium center [60]. It was also shown that 73 Ge NMR, when combined with 13 C NMR, could be used to determine the conformation of organogermanium compounds [48]. The 73 Ge NMR spectrum of 1,4-dimethylgermacyclohexane exhibited two resonances at δ −61.5 and −73.4 ppm, where the resonance at δ −61.5 ppm is assigned to the trans-isomer while the other resonance corresponds to the cis-isomer (Scheme 1).…”

“…The signal at δ −73.4 ppm is also more intense which correlates with the observation that the cis-isomer is the more abundant conformation. Six other methylsubstituted germacyclohexanes were also characterized, as well as the parent unsubstituted germacyclohexane, and it was determined that the exchange of one hydrogen bound to germanium in germacyclohexane with a methyl group in 1-methyl-1-germacyclohexane not only shifts the 73 Ge resonance downfield but reduces the 1 J Ge-H coupling constant [48]. Molecular mechanics calculations combined with 73 Ge and 13 C NMR spectroscopy also indicted that 1-methyl-1-germacyclohexane slightly prefers the axial conformer (Scheme 1) versus the equatorial isomer [62].…”

“…Although the ring size has little influence on the 73 Ge NMR chemical shift in the aforementioned macrocyclic species, this is not true in systems having smaller rings, where the ring size has a pronounced effect on the 73 Ge NMR chemical shift, as indicated by 1,1-dimethyl-1-germacyclopent-3-ene [71] and 1,1dimethylgermacyclohexane [48] that differ in chemical shift by over 50 ppm. Germanium-73 chemical shift values also appear to reflect the two possible conformations (boat or chair) in 3-germabicylco[3.1.0]hexanes (Scheme 3 and Table 13) [50].…”