Abstract: The molecular mechanics calculations (Allinger's MM2 program) was used to study the steric effect of substituents on extraction of metals (Ni, Co, RE) by acidic phosphorus esters. Some parameters for phosphorus which were not included in MM2 were estimated and used to reproduce the known structure of some phosphorus compounds with satisfactory results.
For the evaluation of steric effect of substituents, dialkyl t-butyIphosphate or phosphinate (Ⅱ) was proposed as a model structure for the simulation of the simulation of the steric environment of complexes. The optimum geometry of (II) and phosphorus ester (I) were determined by molecular mechanics program. It was found that the difference of the local steric energy of hydroxyl oxygen in I and II is closely correlated with the degree of the size of substituents and can thus be used as a measurement of the steric effect of the substituents (E_(s,ex)). A series of E_(s,ex) of alkyl and alkoxyl were estimated and used in the multiple regression of extraction data.