Anomalous Ring Proton Shifts in Triphenyl Derivatives of Group IV Elements

Cawley, S.; Danyluk, S.

doi:10.1063/1.1733490

Cited by 7 publications

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“…The concentration dependence is undoubtedly related to the presence of the anisotropic phenyl rings. Striking concentration effects have previously been noted for the ring proton spectra of 4,SiVi and 4,GeVi (50). It was found that an increase in solute concentration led to a down-field shift of the ortho protons and an up-field shift of the meta and para protons.…”

Section: Mediuin Effectsmentioning

confidence: 63%

Proton magnetic resonance spectra of vinylmetallic compounds. Part I. Tetravinyl and triphenylvinyl derivatives of Group IVB elements

Cawley¹,

Danyluk²

1968

Can. J. Chem.

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A study has been made of the proton magnetic resonance spectra for all of the Group IVB derivatives of the series MVi, and 43MVi (4 = phenyl group and Vi = vinyl group). The spectra were measured at 60 MHz as accurately as possible and the assignment of transitions was checked with a variety of supplemental aids including double irradiation, nlultiple quantum transitions, and medium effects. Final, accurate spectral parameters were derived using both iterative and exact comp~~tational methods for solution of the three-spin problem. Excellent agreement was obtained between the sets of parameters determined by the two methods.The clien~ical shifts for both series of compounds display a nunlber of characteristic trends of which the most notable is a displacenlent of the vinyl proton signals to low field with increasing atomic number of the M atom. In each series the largest shift change is noted in going from the carbon to the silicon dcrivative. These deshicldings have been attributed to the enhanced possibility of d,-p, interaction between the central M atoll1 and the vinyl group in higher nlenlbers of the series. Marked changes are also noted for the internal shifts of the vinyl protons down both series of compounds. It is concluded that these changes are principally due to the effects of the M-C bond diamagnetic anisotropy. The trends in internal shifts can be satisfactorily reproduced by the dipole approxin~ation using AX values of 4, 6, 8, 12, and 18 x cnl3 mole-' for the C, Si, Ge, Sn, and Pb-carbon bonds respectively. The signals for the vinyl protons of the &MVi series are all located to low field relative to the MVi, series. This deshielding is satisfactorily accounted for by the effects of the phenyl ring diamagnetic anisotropy in the former series.A linear correlation is observed between the sums of the coupling constants and the electronegativities, Em, of the central M atom for both series of compounds. However, the XJvalues for the &MVi series are all slightly lower than the corresponding s u n~s for the MVi4 series, indicating that the electronegativity of the phenyl group is somewhat larger than for the vinyl group.A significant solvent and concentration dependence is only noted for compounds belonging to the &MVi series. For examplc, the tratis proton of +3GeVi shifts up-field by 4 Hz while the cis proton is displaced down-field by 4 Hz as the concentration of 4,GeVi is increased to 50 mole % in carbon tetrachloride. These changes have been interpreted on the basis of a solute-solute interaction scheme of the type proposed previously for phenyl proton shifts.

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Section: Mediuin Effectsmentioning

confidence: 63%