The Ionic Hydrogen Bond and Ion Solvation. 7. Interaction Energies of Carbanions with Solvent Molecules

Article abstract of DOI:10.1021/ja00220a022

The bonding energy of a water molecule to carbanions range from 11.0 kcal/mol for c-C5H5^- to 13 - 15 kcal/mol for CH2CN^-, CH2CHO^-, and CH2COCH3^- and to 16.2 kcal/mol for HCC^-.Alcohols bond to c-C5H5^- more strongly, by up to 20.6 kcal/mol for the strongly acidic CF3CH2OH, and the attachment energies show an inverse linear correlation with the acidities of the alcohols.The c-C5H5^- ion exhibits unusual behavior in that it bonds to the hydrogen donor H2O more weakly (11.0 kcal/mol) than to CH3CN (15.5 kcal/mol).In contrast, the more localized pyrrolide ion c-C4H4N^- bonds to the two solvents by comparable strength, 15.8 and 15.7 kcal/mol, respectively.These observations indicate a specific N^-*OH hydrogen bonding contribution in c-C4H4N^-*H2O, and/or an unusual C^-*HC type hydrogen bonding contribution in c-C5H5^-*CH3CN.As to structures, correlations between ΔH^o_D and ΔH^o_acid suggest that ligands may hydrogen bond to the ? system of c-C5H5^-, and to the oxygen atoms in CH2CHO^- and CH3COCH2^-.The latter is supported by solvent shell effects in CH3COCH2^-*nH2O.