Proton Magnetic Shielding in the Water Molecule under the Electric Field– Semi-Empirical Calculation of the Proton NMR Shift–

Abstract

The two electron wave function of an OH bond of the water molecule is approximated by a linear combination of the covalent and the ionic type wave functions. The mixing coefficient λ in the gaseous state is determined from the observed dipole moment of the molecule. The proton shift relative to the gaseous state is calculated as a function of λ by a variational method. The values of λ for the water molecules, co-ordinated to Al +++ in the AlCl 3 aqueous solution or to Mg ++ in the crystal of MgCl 2 ·6H 2 O, are empirically determined from the observed shifts. From these values of λ, and the known values of the component of electric field, F // , along the OH bond of the coordinated water molecule, the bond polarizability is estimated. The assumption of constancy for the value of polarizability leads to the result that the shift depends almost linearly on F // .