NUCLEAR MAGNETIC RESONANCE SPECTRA OF METHYLSILANES AND THEIR DERIVATIVES
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Date
1964
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Ohio State University
Abstract
The proton chemical shifts, the vicinal HH, directly-bound $^{29}SiH$ and $^{13}CH$, and some $^{29}SiCH$ coupling constants in more than 20 methylsilyl compounds are reported. These parameters, which have produced the empirical correlations given below, will be discussed with reference to those obtained from silyl and alkyl compounds. $CH_{3^{-}}$ and I- substituents contribute additively to $J_{SiH}$ in SiHXYZ. The $MH_{3}X$ coupling constants (M is C or Si) can be expressed as $J_{MH}^{4} (1+x)$, where the parameter x depends on X, and is approximately the same if M is C or Si. There is a fair correlation between increasing $J_{CH}$ and $J^{SiCH}_{gem}$ in $CH_{3}SiXYZ. CH_{3^{-}}, Br-$ and I- substituents contribute additively to $J_{CH} (CH_{3}SiXYZ)$ and $J^{HH}_{vic} (CH_{3}SiHXY)$, and the latter quantity can also be expressed, as for substituted ethanes, by an equation of the form $J^{HH}_{vic} = J^{0}(1-a\Delta E)$, where $\Delta E = E_{(X)}-E_{(H)}, E_{(X)}$ is the Huggins electronegativity of X, and $J^{0}$ is close to the observed coupling in monomethylsilane. Substitution by $CH_{3^{-}}$ or Br- changes the $\alpha(SiH)$ proton chemical shift additively, and similar effects on the $\beta(CH_{3})$ proton chemical shifts are observed with substitution by $CH_{3^{-}}, Cl-, Br-, or I-$. As in alkyl compounds, $CH_{3^{-}}$ and I- substitution shifts depend substantially on the other groups in the molecule, but Br- and (to a lesser extent) Cl- substitution shifts are fairly constant. The positive F- substitution shifts are particularly interesting. A fair correlation between increasing $\tau(CH_{3}MXYZ)$ and $J_{CH}(CH_{3}MXYZ)$, where M is C or Si, is observed.
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Author Institution: University Chemical Laboratories; Mellon Institute