Correlation Analysis for the Determination of the Steric Effect on N-15 Chemical Shift Depending on Quantum Mechanical Parameters

Abstract

This study is aimed to develop a new set of additive variables for calculating the N15 chemical shift based on quantum mechanical methods for a number of saturated aliphatic amine compounds using the Chem. Office program. Correlation analysis between the experimental N-15 chemical shift with selected variables from two quantum mechanical methods by employing SPSS program were carried out. The relationship between the theoretically calculated chemical shift values of the N15 atom nuclei with the practical values found in the literature were investigated. The two quantum mechanical methods employed to derive parameters used for calculating the N-15 chemical shift, one of them is the semi-empirical Austin method, AM1, and the other representing the ab initio method, density functional theory DFT. The success of the method is determined in terms of the values of correlation coefficient (R) and standard error (SE) as well as the physical meaning of the selected parameters. Good agreement is seen between the practical and theoretical values. A comparison between the two methods was performed to find out the best in calculating chemical shift. The DFT method gave better results