A computer-based approach to describe the 13C NMR chemical shifts of alkanes by the generalized spectral moments of iterated line graphs
A recently introduced strategy to quantitative structure-property relationship studies is used to model the sum of 13C NMR chemical shifts of alkanes. This graph theoretical approach is based on the spectral moments of the iterated line graph sequence (ILGS). The statistical quality of the model developed by using the present approach is compared to those obtained by using spectral moments of the bond matrix or the embedding frequencies of alkanes as independent variables. The embedding frequencies were computed on the basis of the spectral moments of the ILGS. The emphasis of this work is on the structural interpretation of the results. Consequently, the contributions of the different structural fragments of alkanes to the 13C NMR chemical shift sum are computed by the three theoretical approaches. The advantages and disadvantages of the use of these approaches are analyzed on the basis of computational expenditure, i.e. computer time and memory, and the statistical quality, complexity, and structural interpretation of the models developed.
Estrada
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Department of Organic Chemistry, Faculty of Pharmacy, University of Santiago de Compostela, Spain. estrada66@yahoo.com