Charge distributions and chemical effects. XXVII. Molecular energies of carbonyl compounds and ethers, a calculation involving the charges of the bond-forming atoms

Energy calculations are presented for carbonyl compounds and ethers by applying the equation ij = ij 0 + a ij Δq i + a ji Δq j which describes individual bond contributions in terms of electronic charge increments Δq at the bond-forming atoms i and j, relative to atomic charges in selected reference bonds with energies ij 0 . At a molecular level, the sum Σ i Σ j a ij Δq i accounts for virtually the entire energy variations due to charge redistributions accompanying isodesmic structural changes. Coulomb-type interactions between nonbonded atoms play only a minor role in that respect. Using charges derived from 13 C and 17 O nmr shift-charge correlations, calculated and experimental energies agree within 0.16 kcal/mol (average deviation).