Abstract
The enthalpies of interaction of tetrahydrofuran (THF) and 2,5-dimethyltetrahydrofuran (Me2THF) with 0.03M benzene solutions of poly(styryl)lithium (PSLi) and poly(isoprenyl)lithium (PILi) have been measured as a function of R ([THF]/[Li]) at 25°C using high dilution solution calorimetry. At low R values (ca. 0.2) the enthalpy of interaction of THF with PILi (-5.8 kcal/mole) is more exothermic than with PSLi (-4.5 kcal/mole). However, the decrease in enthalpy for Me2THF versus THF is larger for PILi (3.2 kcal/mole) than for PSLi (2.2 kcal/mole) at low R values. The enthalpies decrease rapidly with increasing R values for PILi, but are relatively constant for PSLi. It is suggested that THF interacts with intact dimer for PILi, but for PSLi this base coordinates to form the unassociated, THF-solvated species.
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