Abstract
Some calculations of the [13]C and [15]N shielding constant are carried out using CNDO/S and INDO/S procedures within the GIAO-MO framework described by Pople. These are compared with the experimental results, in the form of [13]C chemical shifts with respect to benzene and in the form of [15]N chemical shifts with respect to nitromethane, CH[3]NO[2]. In Chapter one, several current theories of magnetic shielding are briefly reviewed. Chapter two presents a survey of various semi-empirical molecular orbital treatments of magnetic shielding constant. The approximations introduced and the MO theory used are also described in Chapter two.Chapter three presents [13]C, [15]N and [19]F chemical shifts and their anisotropies were calculated. A reasonable correlation between the calculated and experimental chemical shifts, compared by means of least square fit, is obtained for most of the molecules considered.