Lithium and Cesium Ion-Pair Acidities of Some Terminal Acetylenes and Aggregation in Tetrahydrofuran¹

The equilibrium lithium acidities in THF have been determined for 4-ethynylbiphenyl, EB (pK 21.5−22.3), 3,3,3-triphenylpropyne, TPP (pK 22.3−22.7), and 1-ethynyladamantane, EA (pK 23.7). Ion pairs of (4-ethynylbiphenylyl)lithium are aggregated in the concentration range from 10^-4 to 10^-3 M, with an average aggregation number of 2.5. (3,3,3-Triphenylpropynyl)lithium ion pairs are partially aggregated at concentrations from 10^-5 to 10^-3 M; the average aggregation number is 1.2. Cesium acidities in THF have been determined for 3,3,3-triphenylpropyne (pK 29.1−29.9) and 1-ethynyladamantane (pK 31.56). The average aggregation number of (3,3,3-triphenylpropynyl)cesium ion pairs is 6.2 at concentrations of 10^-4−10^-3 M.