A Density Functional Theory Study of Structure of Phosphonic Acid

Abstract

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