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An ab initio and force field study on the conformation and chain flexibility of the dichlorophosphazene trimer
Author(s) -
Jaeger Raimund,
Vancso G. Julius
Publication year - 1996
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/mats.1996.040050404
Subject(s) - ab initio , chemistry , trimer , dihedral angle , ab initio quantum chemistry methods , molecular geometry , bond length , van der waals force , charge density , force field (fiction) , conformational isomerism , computational chemistry , basis set , delocalized electron , molecular physics , crystallography , density functional theory , molecule , physics , hydrogen bond , crystal structure , dimer , quantum mechanics , organic chemistry
Ab initio molecular orbital calculations have been used to study the conformation, valence electron charge density, and chain flexibility of a dichlorophosphazene trimer (CH 3 [NP(Cl 2 )] 3 CH 3 ). The calculations were carried out at the restricted Hartree‐Fock level with the 6–31 G * basis set. The dichlorophosphazene trimer adopts a planar transcis conformation. The valence electron charge distribution indicates strong charge separations along the backbone of the molecule, and is in agreement with Dewar's island delocalization model for bonding in linear and cyclic phosphazenes. In order to determine the height of the torsional barrier (2,5 kcal/mol), the torsional potential of a central PN bond of the trimer was studied with a rigid rotor scan and geometry optimizations of selected rotamers. The flexibility of the PNP bond angle contributes significantly to the chain flexibility. Based on the results of the ab initio calculations, an empirical force field for the dichlorophosphazene trimer was developed. The energy expression includes bond stretch, angle bend, electrostatic, van der Waals, and torsional potential terms. A relaxed scan with the force field achieves good agreement with the ab initio results for the torsional potential in the vicinity of the stable conformation, and an excellent agreement with the ab initio results on changes in the P 2 N 2 P 3 bond angle and the N 1 P 2 N 2 P 3 dihedral angle during a full rotation around the N 2 P 3 bond.