A Density Functional Theory Study of Structure of Phosphonic Acid

Document Type : Research Paper




The molecular structure of the stable conformation of phosphonic acid in gas phase has been
computed by employing complete geometry optimization in Density Functional Theory
(DFT) methods. The methods used for calculations are B3LYP, BP86 and B3PW91 that have
been studied in two series of basis sets: D95** and 6-31+G(d,p) for hydrogen and oxygen
atoms; LANL2DZ for phosphorus. Bond lengths and angles generally agree with the limited
prior theoretical and experimental values. Phosphonic acid exhibits a minimum-energy
conformation in which the acidic hydrogens are oriented toward the phosphoryl oxygen and
the distance from it, nearly 2.7-2.8 A. The conformation of phosphonic acid may be
described on the basis dipole-dipole interactions plus relatively small internal hydrogen
bonding and steric effect. In contrast to earlier studies, little conformational evidence of
"anomeric" effects is found in this compound.