The Basicity of C¹³-H Coupling Constants of Certain Acetals, Ketals, and Ortho Esters

Mechanism and catalysis for hydrolysis of acetals, ketals, and ortho esters

“…Fourth, hydrolysis of those acetals and ketals of abnormally low basicity occurs with relatively small solvent isotope effects (note entries A: 24,25,[47][48][49][50][51][52][53]. This is consistent with the behavior of ortho esters which ordinarily have basicities substantially less than those for simple acetals (Table I ) .…”

“…The effects of structure on basicity of acetals, ketals, and ortho esters are accounted for quite nicely on the basis of polar effects of the various substituents involved. [23][24] In fact, for those cases in which comparison is possible, the measured values of pKa agree quite well with values calculated prior to these measurements on the basis of a linear free-energy relationship and effects of polar substituents.25 This result strongly suggests that double bond-no bond resonance, which should dramatically reduce the basicity of ortho esters and orthocarbonates relative to acetals and ketals, is not important for these compounds.26…”

“…Second, rate constants for hydrolysis of acetals, ketals, and ortho esters increase with increasing electron donation from polar substituents located in that alkoxy function which does not leave in the rate-determining step (entries [22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

Reactions of Ortho Esters Which Result in Carbon-Oxygen and Carbon-Halogen Bond Formation

“…The pK a values estimated in this way are -5.4 for dimethyl acetal, -7 for triethyl orthoformate, -7.6 for triethyl orthobenzoate, and -8.5 for tetraethyl orthocarbonate. These values are in excellent agreement with values calculated from infrared O-D stretching frequency measurements on deuteromethanol solutions of the ortho esters (222). Using the measured k K + and estimated Κ Λ values, Eq.…”

Negotiated Identities of Chemical Instrumentation

“…Thus, answering the question ‘What is an NMR spectrometer?’ becomes increasingly difficult outside of its historical and cultural context. The NMR spectrometer used by Norman Allinger in 19564 to investigate the structure of helvolic acid was definitely physically different from the NMR spectrometer used by Pletcher and Cordes in 196719 when they examined the basicity and coupling constants of three groups of compounds. But, the instrument did not undergo only physical changes.…”