Gauging the donor ability of the C-Si bond.: Results from low-temperature structural studies of gauche and antiperiplanar β-trimethylsilyl-cyclohexyl esters and ethers by use of the variable oxygen probe

A plot of C-OR bond distance against pK(a)(ROH) for esters and ether derivatives of the antiperiplanar beta-silyl alcohol (4) has a slope of -5.3 x 10(-3). This represents a stronger response of the C-OR distance than was observed for the corresponding gauche beta-silyl alcohol (5) and its derivatives. This result is consistent with the greater donor ability of a C-Si bond compared with a C-C bond. Comparison of these plots with those previously reported for derivatives (3) of tetrahydropyran-2-ol reveals that a C-Si bond is a weaker donor than an oxygen non-bonded pair of electrons. An estimate of the pK(a) value for 2,4-dinitrobenzenesulfenic acid (14) was derived from these plots.