Thermochemistry aldol reaction

After this chapter had been completed, there appeared a paper describing the first determination of the thermochemistry of an aldol reaction of a preformed enolate (E. M. Arnett, F. J. Fisher, M. A. Nichols and A. A. Ribeiro, J. Am. Chem. Soc., 1989, 111, 748). The enthalpy of reaction of the hexameric lithium enolate of pinacolone with pivalaldehyde in hexane at 25 C is -30.19 0.76 kcal mol. With one equivalent of various added ligands, enthalpies of reaction are -17.94 0.36 kcal mol in tetrahydrofu-ran (THF) -20.85 0.72 kcal mol in tetramethylethylenediamine (TMEDA) and -19.05 0.44 kcal mol in dimethoxyethane (DME). The product is believed to be a tetrameric lithium aldolate in each case. In view of the discussion given in this section, these reactions are surprisingly exothermic. Note, however, that one equivalent of THF makes the reaction about 10 kcal mol less exothermic. The enthalpy of reaction in pure THF has yet to be determined experimentally. 

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