Delocalized Carbanions. IV. < sup> 1 Structural Studies on the Alkali Metal Derivatives of 1- and 2-Methylnaphthalene

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Carbon–metal bonding in 1- and 2-naphthylmethyllithium, -sodium, and -potassium was investigated using pmr spectroscopy. In tetrahydrofuran (THF), the chemical shifts of the ring protons of the carbanions relative to naphthalene (δN) increase in the upfield direction in the order Li < Na < K. They were found to follow the equation, where is the cation radius and δN∞ is the extrapolated chemical shift of the corresponding proton in the free anion. The term is interpreted as the amount of C–M bond delocalization in the contact ion pair. Appreciable barriers to rotation about the ring–methylene bonds in the anions show that the partial delocalization is not due to rapid equilibria between ionic and covalent forms. Lack of cation dependence of the spectra of the Li and Na compounds in hexamethlylphosphoramide (HMPA) indicated the presence of solvent separated ion pairs or free ions in this solvent. Comparison of the spectra of the Li compounds in ether and THF led to the conclusion that in ether the Li+ ions may be allylically coordinated to the methylene carbon and a ring carbon. © 1972, American Chemical Society. All rights reserved.

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Journal of the American Chemical Society