jo026022g_si_001.pdf (50.56 kB)
Structures and Aggregation States of Fluoromethyllithium and Chloromethyllithium Carbenoids in the Gas Phase and in Ethereal Solvent
journal contribution
posted on 2002-10-04, 00:00 authored by Lawrence M. Pratt, Bala Ramachandran, James D. Xidos, Christopher J. Cramer, Donald G. TruhlarUsing high-level quantum mechanical calculations and various models to account for solvation
effects, monomers and dimers of fluoromethyllithium and chloromethyllithium carbenoids are
studied in the gas phase and in dimethyl ether solvent. A combination of explicit microsolvation
and a continuum reaction field is required to account fully for the structural and energetic effects
of solvation. One important effect of solvent is the stabilization of charge-separated structures in
which the lithium−halogen distance is much greater than in the gas-phase structures. At the most
complete level of theory the 173 K standard-state free energy of dimerization of fluoromethyllithium
in dimethyl ether is predicted to be −0.9 kcal mol-1, while that for chloromethyllithium in the
same solvent is predicted to be 3.7 kcal mol-1. This suggests that, under typical experimental
conditions, dimers of chloroalkyllithiums will not be observed, while dimers of fluoroalkyllithiums
may contribute to the equilibrium population at a detectable level.