Order parameters and molecular shapes of phosphonic acid dialkyl esters in a uniaxial hydrophobic environment. A theoretical study

Abstract

The conformational behaviour of phosphonic acid dialkyl ester (PAE) molecules in a uniaxial hydrophobic environment was studied using the Monte Carlo method with the well-known Metropolis algorithm. The influence of the surrounding molecules on ordering processes of the intrinsic PAE molecules was taken into account by a molecular field. The intramolecular energy was calculated using 6–12 atom-atom and torsion potential functions.

Conformations were analysed using torsion angle distributions, segment and bond order parameters. The order parameters of the C-H bonds are compared with experimental results of²H NMR.

Further a general method of determining the effective shape of a molecule is presented. The shape is defined by probability distribution for finding atomic coordinates within volume elements during a Monte Carlo run. Thus the asymmetry of a molecule can be visualized. PAE molecules studied show a positive asymmetry in all cases.