Structural assignment of 2,6- and 2,7-disubstituted naphthalenes and prediction of 13C nuclear magnetic resonance chemical shifts: applications of topology and two-dimensional NMR spectroscopy

Abstract

Unambiguous assignments of monocarboxymethylnapthalenes isolated as oxidation products of dimethylnaphthalenes by Pseudomonas putida, a bacterial strain, were made using two-dimensional nuclear Overhauser enhancement correlation spectroscopy (NOESEY). The two-dimensional long-range heteronuclear correlation NMR technique was also utilized for the assignment of quaternary carbons in the naphthalene system. In addition, we describe methods for prediction of 13C NMR chemical shifts of 2,6- and 2,7-disubstituted naphthalenes using topological approach. The method involves computation of molecular descriptors from topological representation of molecule, namely Wiener (W) and Szeged (Sz) indices. The results have shown that W and Sz indices can be successfully used for predicting 13C NMR chemical shifts and that Σ 13Cn can be used as a molecular property which in turn can be modeled by both W and Sz indices successfully.