โ Scribed by John. N. C. Walton
No coin nor oath required. For personal study only.
The 29Si satellites were observed in the EPR spectra of 3-trimethylsilylprop-2-yny1, 1-trimethylsiloxyprop-2-ynyl and trimethylsiloxymethyl radicals. Comparison of the experimental values with spin densities calculated by semi-empirical MO methods led to a value of 810 G for Qsi. The magnitude and positive temperature dependence of the ~( ' ~s i )
values in the siloxy-substituted radicals showed that their preferred conformations are staggered with the silicon atom in the nodal plane of the orbital containing the unpaired electron. This contrasts with the analogous P-trialkylsilylethyl radicals, which adopt eclipsed conformations. The rotation barrier about the 'C-a-0 bond in trimethylsiloxymethyl radicals was estimated to be 3.8 kcal mol-'. The preference of P-oxamethyl radicals for the staggered conformation was attributed to the comparatively large stabilization due to the interaction of the unpaired electron with the adjacent oxygen, and an attempt was made to quantify this effect.
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