Low-temperature X-ray structural studies of the ester and ether derivatives of cis- and trans-4-tert-butyl cyclohexanol and 2-adamantanol: application of the variable oxygen probe to determine the relative sigma-donor ability of C-H and C-C bonds.
Results of low-temperature X-ray structural studies for five cis-, and three trans-4-tert-butyl cyclohexanol, and six 2-adamantanol ester and ether derivatives are reported. Plots of C-OR bond distance against pKa(ROH) for derivatives of axial alcohol (5), equatorial alcohol (6) and 2-adamantanol derivatives (7) give slopes of -2.77 x 10(-3), -2.86 x 10(-3) and -3.05 x 10(-3), respectively. Given that the relative differences in the slopes are modest, no clear distinction can be made about the relative sigma-donor ability of a C-H bond and a C-C bond.