title: Preorganized Hydrogen Bond Donor Catalysts: Acidities and Reactivities.
abstract: Measured DMSO pKa values for a series of rigid tricyclic adamantane-like triols containing 0-3 trifluoromethyl groups (i.e., 3(0)-3(3)) are reported. The three compounds with CF3 substituents are similar or more acidic than acetic acid (pKa = 13.5 (3(1)), 9.5 (3(2)), 7.3 (3(3)) vs 12.6 (HOAc)), and the resulting hydrogen bond network enables a remote γ-trifluoromethyl group to enhance the acidity as well as one located at the α-position. Catalytic abilities of 3(0)-3(3) were also examined. In a nonpolar environment a rate enhancement of up to 100-fold over flexible acyclic analogs was observed presumably due to an entropic advantage of the locked-in structure. Gas-phase acidities are found to correlate with the catalytic activity better than DMSO pKa values and appear to be a better measure of acidities in low dielectric constant media. These trends are reduced or reversed in polar solvents highlighting the importance of the reaction environment.
authors.affiliation: Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Masoud
authors.initials: M
authors.lastname: Samet
authors.affiliation: Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Kass
mesh_terms: D000143:Acids / Q000737:chemistry*; D000218:Adamantane / Q000031:analogs & derivatives* / Q000737:chemistry*; D002384:Catalysis; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D012997:Solvents / Q000737:chemistry
chemical_list: D000143:Acids; D006845:Hydrocarbons, Fluorinated; D012997:Solvents; D000218:Adamantane; D004121:Dimethyl Sulfoxide