Carbon-13 Chemical Shift Tensors in Aromatic Compounds. 4. Substituted Naphthalenes

The principal values of the ¹³C chemical shift tensor were measured for the aromatic carbons of 1,4,5,8-tetramethylnaphthalene, 1,2,3,6,7,8-hexahydropyrene, and pyracene using the variable angle spinning technique. Ab initio calculations of the complete shielding tensors are also reported and provided the orientation of the principal values in the molecular frame. Good agreement between theory and experiment is obtained. The chemical shift principal values and orientations of these substituted naphthalenes correspond to those found in naphthalene; the observed differences can be rationalized in terms of the strain introduced by the alkyl substituent. In the naphthalenic derivatives studied, the bridgehead carbons exhibit relatively extensive π-electron delocalization not found in some bridgeheads in more highly condensed aromatic systems. © 1992, American Chemical Society. All rights reserved.

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