Theoretical Comparison of Formic Acid and the Formate Ion

Abstract

Ab initio SCF MO and CI calculations are reported for formic acid HCOOH and the formate ion HCOO⁻. A simplified theoretical treatment for the salts of formic acid is considered in which a bare positive charge without an accompanying AO basis function serves as a model for the associated metal cation. The calculations suggest that the formation of an OHO bridge occurs in certain symmetric nuclear arrangements, even for monomeric HCOOH; the stability of the system is subsequently shown to be increased by the migration of the acidic hydrogen toward one of the oxygens and away from the other, thereby producing the known nonsymmetric equilibrium geometry of the acid. The influence of the acidic hydrogen is also apparent in the comparison of the spectra of HCOOH and HCOO⁻, causing the displacement of transitions to a ^3,1B pair of states to considerably shorter wavelengths than are observed for the corresponding transitions in the anion. Calculated molecular properties of formic acid for various SCF and CI treatments are also reported and comparison with pertinent experimental data indicates certain definite advantages in employing CI techniques to improve the SCF ground‐state electronic distribution.