Solid-state 13C NMR measurements in methoxynaphthalenes: Determination of the substituent chemical shift effects in the principal values

The principal values of the ¹³C chemical shift tensor are measured in 1-methoxy-, 2-methoxy-, 1,4-dimethoxy-, 2,6-dimethoxy-, and 2,7-dimethoxynaphthalene using the triple echo version of the 2D magic angle turning (MAT) experiment. In the case of 1-methoxynaphthalene, a room-temperature liquid, the experiment was performed at low temperature. Assignments of the measured principal values of the chemical shift tensors to the individual carbons are made by both comparison of the solid-state isotropic chemical shift to the known solution values and comparison of the experimental principal values to the results of ab initio calculations of the chemical shielding tensor. The methoxy group substituent chemical shift parameters for each of the three components is determined relative to the parent unsubstituted naphthalene for the protonated and ipso carbons. The substituent parameters are very similar to those previously observed for methoxy substituted benzenes. The bond populations, determined using ab initio methods, are used to show how sensitive the orientation of the in-plane components of the chemical shift tensor is to the electronic distribution in aromatic systems.

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Author Julio Cesar Facelli Biostatistics & Bioinformatics, Division of Translational Bi ...