Twenty-four aryl orthocarbonates of formula (Aro)(4)C, (ArO)(2)C(OAr’)(2), or (ArO)(3)COAr’ have been made by coupling of the copper phenoxides with carbon disulfide, and their hydrolyses have been examined in 60% water-40% acetonitrile (I = 1.00 M, KCl) at 70.0 degrees C. Their hydrolysis by general acid catalyzed and, in the case of (ArO)(3)COAr’ when Ar’= p-nitrophenyl and p-cyanophenyl, spontaneous processes yields aryl carbonates. The initial, rate-determining event for both processes is the cleavage of the bond between the central carbon and the least basic phenoxy group : with mixed orthocarbonates of phenols differing in pK by <1 unit, parallel pathways are observed. The spontaneous reactions of (X-C6H4O)(3)C-O-p-C6H4NO2 and (X-C6H4O)(3)C-O-p-C6H4CN where the sigma value of X varies from -0.23 to 0.22 are 4-10 times slower than reactions of p-nitrophenyl tetrahydropyrans reported in the literature and give rise to nonlinear Hammett plots. However, plots against the pK(a) of X-C6H4OH are linear, and the derived beta(reaction center) values indicate substantial buildup of positive charge on the central carbon atom. A similar plot is obtained for the spontaneous reactions of five azides (XC(6)H(4)O)(3)CN3 for which common ion inhibition experiments have been performed. The derived selectivities (M(-1)) of the tris(aryloxy)carbenium ion intermediates between azide ion and water vary from 8.5 X 10(3) to 6.6 X 10(3) as the sigma value of X changes from -0.28 to 0.06. The lifetime of the tris(aryloxy)carbenium ion intermediates in water is therefore likely to be > 10(-6) s. The slow formation and slow hydrolysis of tris(aryloxy)carbenium ions suggests that (in the formation direction) development of conjugative stabilization lags behind carbon-oxygen bond cleavage and (in the hydrolysis direction) precedes carbon-oxygen bond formation. The stereochemistry of tetraaryl orthocarbonates immediately suggests reasons why this should be so.