Study of the Conformational Dependence of C-13 Chemical Shifts of Cycloalkanes using Regression Analysis Method

The effect of spatial arrangement on carbon-13 (130) chemical shifts of cycloalkanes has been investigated. The parameters used for calculating the 130 chemical shifts are based on two principles. The p-character which is represented by the number of primary, secondary and tertiary carbons at alpha-position, and the steric effect of the alkyl groups and hydrogen in different location which induce proton interactions between the considered carbon and the other carbons of the molecule at alpha, beta, gamma,.., etc positions. General and individual sets of coefficients for cyclohexanes, cis-and trans-decalin, and for structural isomers of perhydrophenanthrene (PHP) and perhydroanthracene (PHA) have been derived. The values of the coefficients of the parameters are obtained by employing linear regression analysis method. The predicted chemical shifts by using the general sets of coefficients gave higher deviation from the empirical values. The parameters are proved to be sensitive to change in spatial arrangement since 130 chemical shifts of multiple rings compounds can be calculated from the regression analysis results of monocyclic compounds and vise versa, and deviations are noticed only in positions that discriminate the conformation of a specific compound and/or involved in large steric interactions. Carbon-13 chemical shifts have been calculated for a number of hypothetical compounds, which may exist (or compounds of like structure) in coal, oil and natural products. The spectrum of these compounds has been plotted theoretically.