Measure what is measurable, and make measurable what is not so! This timeless quotation by Galileo forms the basis of all quantitative understanding, including asymmetric organocatalysis. We report pKa values for 15 chiral Brønsted acid catalysts in DMSO solutions (see scheme): the strongest acids were bis‐sulfonyl/sulfuryl imides (pKa=1.7–1.9) followed by phosphoric acids/amides (pKa=2.4–4.2). A new class of chiral Brønsted acids, tetrakis‐perfluoroalkyl analogues of TADDOLs (TEFDDOLs) have pKas from 2.4 to 5.7.

The synthesis of six enantiopure α,α,α',α'-tetrakis(perfluoroalkyl/aryl)-2,2'-dimethyl-1,3-dioxolane-4,5-dimethanols (TEFDDOLs), by addition of perfluorinated organolithium reagents or Ruppert's reagent (TMS-CF(3)) to isopropylidene tartaric dichloride, is reported. X-ray crystal structures of the TEFDDOLs alone or in complexes with H-bond acceptors such as water and DABCO revealed that this new class of highly fluorinated chiral 1,4-diols forms distinct intra- and intermolecular H-bond patterns. Intramolecular OH-OH bonding accounts for the relatively high acidity of the perfluoroalkyl TEFDDOLs (pK(a) in DMSO: tetrakis-CF(3), 5.7; tetrakis-C(2)F(5), 2.4). For the tetrakis(perfluorophenyl) TEFDDOL, a quite unusual "pseudo-anti" conformation of the diol, with no intramolecular (and no intermolecular) OH-OH bonds, was found both in the crystal and in solution (DOSY and NOESY NMR). The latter conformation results from a total of four intramolecular OH-F(aryl) hydrogen bonds overriding OH-OH bonding. Due to their H-bonding properties, the TEFDDOLs are promising new building blocks for supramolecular and potentially catalytic applications.