| Abstract
| - The gas-phase acidities ΔG°acid of some 20 amides/enols of amides RNHCOCHYY‘/RNHC(OH)CYY‘ [R = Ph, i-Pr; Y, Y‘ = CO2R‘, CO2R‘ ‘, or CN, CO2R‘, R‘, R‘ ‘ = Me, CH2CF3, CH(CF3)2], theN-Ph and N-Pr-i amides of Meldrum's acid, 1,3-cyclopentanedione, dimedone, and 1,3-indanedione,and some N-p-BrC6H4 derivatives and of nine CH2YY‘ (Y, Y‘ = CN, CO2R‘, CO2R‘ ‘), including thecyclic carbon acids listed above, were determined by ICR. The acidities were calculated at the B3LYP/6-31+G*//B3LYP/6-31+G* level for both the enol and the amide species or for the carbon acid andthe enol on the CO in the CH2YY‘ series. For 12 of the compounds, calculations were also conductedwith the larger base sets 6-311+G* and G-311+G**. The ΔG°acid values changed from 341.3 kcal/mol for CH2(CO2Me)2 to 301.0 kcal/mol for PhNHC(OH)C(CN)CH(CF3)2. The acidities increasedfor combinations of Y and Y‘ based on the order CO2Me < CO2CH2CF3< CN, CO2CH(CF3)2 for asingle group and reflect the increased electron-withdrawal ability of Y,Y‘ coupled with the abilityto achieve planarity of the crowded anion. The acidities of corresponding YY‘-substituted systemsfollow the order N-Ph enols > N-Pr-i enols ≫ CH2YY‘. Better linear relationships between ΔG°acidvalues calculated for the enols and the observed values than those for the values calculated for theamides suggest that the ionization site is the enolic O−H of most of the noncyclic trisubstitutedmethanes. The experimental ΔG°acid value for Meldrum's acid matches the recently reportedcalculated value. The calculated structures and natural charges of all species are given, and thechanges occurring in them on ionization are discussed. Correlations between the ΔG°acid valuesand the pKenol values, which are linear for the trisubstituted methanes, excluding YY‘ = (CN)2 andnonlinear for the CH2YY‘ systems, are discussed.
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