SEMI EMPIRICAL AND AB-INITIO CALCULATIONS ON SOME BINARY LIQUID MIXTURES
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Publisher:Ohio State University
Theoretical conformation studies are carried out on the following binary mixtures of weakly bonded complexes: Formamide - Water, Formamide - Methanol. Acetonitrile - Water and Acetonitrile Methanol. Dipole moment and quadruple coupling constant are the physical parameters used to judge the validity of the conformations identified after the total energy as well as the hydrogen bonding energy are minimized. Nuclear Quadruple Coupling constant is one of the one-electron properties which can be used as a sensitive parameter in determining the exact charge distribution in any polyatomic molecular system. Electric field gradient(EFG) is calculated at the site of Nitrogen nucleus using both semi-empirical LCAO-MO-SCF and ab-initio methods. Several conformers are chosen for the study with Slater type of orbitals as the basis functions at the semi-empirical levels and Gaussian 3-21G, 3-31G, 6-31G basis sets are used at the ab-initio level. The value of these Quadruple coupling constants, thus calculated theoretically, is compared with the experimental value for arriving at the correct conformation of the molecular system. Dipole moments are also calculated for the above systems for various conformations and compared with the experimental values. Variation of dipole moments with hydrogen bonding distance is also studied. Potential energy curves are also drawn by varying the hydrogen bonding distance in each case. Both hydrogen bonding energy and total energy are used as criterion for deciding the correct conformation in each system. The potential energy curve for the binary complex of planar structure with single hydrogen bond is shown in Fig. 1 at the minimal basis set, by varying the hydrogen bond distance 1A to 4A in steps of 1A. The interaction energy is found to be 8 Kcal per mole for this conformer.
Author Institution: Department of Physics, Presidency College; Department of Physics, Indian Institute of Technology
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