Moreover, the formed 2-oxabicyclo[2.2.2]octane core resembled well the para-substituted phenyl ring, as the geometric parameters r, d, φ1, and φ2 remained very similar. The key characteristics of both cores and their superposition are shown in Figure . The acidity of functional groups. We also studied the influence of the replacement of the methylene group for oxygen atom in the bicyclo[2.2.2]octane skeleton on the electronic properties. For that, we experimentally measured pKa values of isomeric 2-oxabicyclo[2.2.2]octane carboxylic acids 37 and 43, bicyclo[2.2.2]octane carboxylic acid 62, and para-methyl benzoic acid (61) as a reference (Figure ). Replacement of the methylene group in 62 for the oxygen atom at the distal γ-position dramatically increased its acidity from pKa=5.6 to 4.4 (37). However, analogous replacement at the β-position increased the acidity even more to pKa=4. 1 (43).