Some calculations of solvent dependencies of nuclear spin couplings.

The present work falls into two main parts. Firstly, a theoretical investigation of some solvent dependencies of nuclear spin-spin couplings. Secondly, some calculations of (N-C) couplings by various MO approaches. In. chapter 1, the theory of nuclear spin-spin couplings is presented. In chapter 2, a description of molecular orbital (MO) theory with various levels of approximations is applied to the calculations of nuclear spin couplings. In the first part of the present research work, presented in chapter 3, the 'solvaton model', the theoretical detail of which is presented in section (3. 2) is adopted in order to study quantitavely non-specific medium effects on nuclear spin couplings. Self consistent field (SCF) wavefunctions are obtained by the semi empirical intermediate neglect of differential overlap (INDO) approximation in terms of the sum over states (SOS) and self consistent perturbation theory (SCPT) methods. The calculations comprise all of the contributing terms to coupling constants. Some couplings in fluoroethylenes, fluoromethanes, Acrylonitrile and Imidazole, are selected to be the subject of this investigation due to the availability of some experimental solvent effect data. Tables of the theoretical and experimental results are presented and discussed. Some simple nitrogen containing molecules are chosen for study in order to investigate solvent effects on [1]J(N-C) and [1]J(N=C) values of these compounds. The couplings considered are presented as a function of the dielectric constant of the medium. The second part of this work appears in chapter 4, it relates to the calculation of (NC) couplings for some simple isolated nitrogen compounds by the INDO-SCPT, INDO-SOS-fixed atomic integral, INDO-SOS-varied integral and (INDO/S)-SOS procedures. Comparison between the calculated data and the available experimental ones are presented in Table (4.2) and discussed in this chapter