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Charge distribution in substituted allyl-alkali metal compounds by 13C NMR

1978; Elsevier BV; Volume: 159; Issue: 3 Linguagem: Inglês

10.1016/s0022-328x(00)93801-4

1872-8561

S. Bywater, D. J. Worsfold,

Inorganic and Organometallic Chemistry

The 13C NMR spectrum of 5,5-dimethylhexen-2-ylmetals and 2,5,5-trimethylhexen-2-ylmetals have been measured where the metal (M) is Li, Na, K, Rb, Cs, Hg and Si(CH3)3. When M  Li, the solvents have been C6D6, diethyl ether, tetrahydrofuran, and dimethoxyethane. Substantial changes of the chemical shifts of the α, β and γ carbons occur in the alkali metal compounds as the counter ions vary, and all are changed relative to the parent hydrocarbon. Very small temperature effects are found down to −80°C. If allowance is made for a change in hybridization of the α carbon, the sums of these chemical shift changes from the parent hydrocarbon are similar for all the alkali metals. It is suggested that all these compounds are delocalized ionic compounds, with the charge in the caesium compound favouring slightly the α position over the γ position. But as the counter ion becomes smaller the charge resides more on the α position. In contrast the behaviour of the Si and Hg compounds is more that expected of covalent compounds.