Protonated Benzofuran, Anthracene, Naphthalene, Benzene, Ethene, and Ethyne: Measurements and Estimates of pKa and pKR

摘要: Aqueous solvolyses of acyl derivatives hydrates (water adducts) anthracene and benzofuran yield carbocations which undergo competitive deprotonation to form the aromatic molecules nucleophilic reaction with water give hydrates. Trapping experiments azide ions rate constants k(p) for k(H2O) based on "azide clock". Combining these (a) H(+)-catalyzed hydrate carbocation (b) hydrogen isotope exchange molecule (from literature) yields pK(R) = -6.0 -9.4 pK(a) -13.5 -16.3 protonated benzofuran, respectively. These pK values may be compared -6.7 naphthalene (1-hydroxy-1,2-dihydronaphthalene), extrapolated from measurements by Pirinccioglu Thibblin acetonitrile-water mixtures, -20.4 2-protonated combining an constant. The differences between correspond pK(H2O), equilibrium constant hydration (pK(H2O) - pK(a)). For pK(H2O) +13.7 +7.5 compare independent estimates +14.2 +7.4. benzene, -24.3 is derived assigned value reverse close limit solvent relaxation. this calculated gives -2.4 -2.1 benzenes forming 1,2- 1,4-hydrates, Coincidentally, protonation benzene similar those ethylene acetylene (Lucchini, V.; Modena, G. J. Am. Chem Soc. 1990, 112, 6291). Values ethyl vinyl cations (-24.8) thus in same way as that benzenonium ion. appropriate then -39.8 -29.6 cations,