2-Pentanone and 2-pentanone-l,l,l-d3 were treated with three-fold excesses of lithium diiso- propylamide (LDA) or lithium hexamethyldisilazide (LHMDS) in tetrahydrofuran (THF) with and without hexamethylphosphoric triamide

2-Pentanone and 2-pentanone-l,l,l-d3 were treated with three-fold excesses of lithium diisopropylamide (LDA) or lithium hexamethyldisilazide (LHMDS) in tetrahydrofuran (THF) with and without hexamethylphosphoric triamide (HMPA, 3 mol per mol of base) at temperatures ranging from 24 to — 70 °C. The deuterium kinetic isotope effects calculated from the product ratios (mea­ sured by GLC as trimethylsilyl enol ethers) showed a range of temperature dependences: none (LDA in THF), attenuated with A ĵA ̂= 2.53 (LHMDS in THF), and normal with /1H//1D~0.6 indicating moderate tunneling (LDA and LHMDS in THF-HMPA). The variation in temperature dependence is attributed to reaction via multiple base species in which HMPA affects the equilibria between the base species.