Acidities of hydrocarbons and sulfur-containing hydrocarbons in dimethyl sulfoxide solutions

The relative pK/sub a/ values in Me/sub 2/SO solution of 13 hydrocarbons that form carbanions with highly dispersed negative charges on deprotonation were found to differ from literature relative ion-pair acidities in cyclohexylamine (CHA) by only +/-0.7 unit, or less, when the ion pair pK/sub a/'s were anchored to the pK/sub a/ of 17.9 for 9-phenylfluorene in Me/sub 2/SO. The relative pK/sub a/'s for phenylacetylene, cyclopentadiene, and indene were found to be 2.4, 2.7, and 0.9 units higher, respectively, in Me/sub 2/SO than in CHA. Higher relative pK/sub a/'s were also observed for PhCH/sub 2/SO/sub 2/Ph, PhSO/sub 2/CH/sub 3/, and the PhSO/sub 2/CH/sub 2/Me, by 1.9, 2.7, and 2.8 units, respectively, and for 2-phenyl-1,3-dithiane, 2-(p-phenylphenyl)-1,3-dithiane, 4-methyl-2,6,7-triathiabicyclo(2.2.2)octane, and 1,3-dithiane, by 0.4, 0.65, 0.8, and approx.1.9 units, respectively. The apparent higher relative acidities for these compounds in CHA is probably caused by stronger ion pairing or aggregation of the ions derived therefrom than for the hydrocarbon indicator ions with which they are being compared.