3-((Benzyloxy)carbonyl)bicyclo[1.1.1]pentane-1-carboxylic Acid

The compound 3-((benzyloxy)carbonyl)bicyclo[1.1.1]pentane-1-carboxylic acid was successfully synthesized. High-quality crystals were obtained, and its X-ray structure was solved and refined by Hirshfeld atom refinement using custom aspherical scattering factors with the Olex2/NoSphereA2 package. Hydrogen bonding interactions lead to head-to-head carboxylic acid dimer formation. A positional disorder for the bridging H-atom was detected and modeled to two parts in a 0.85:0.15 ratio. Detailed comparison with a neutron diffraction study of benzoic acid at the same temperature (100 K) demonstrates that the E–H-bond distances in the title compound are in excellent agreement (differing less than 1%) and the displacement ellipsoids volumes to the model are also in excellent agreement to the neutron diffraction structure. Moreover, both the variation in refined disorder occupancy and differences in C=O and C–O lengths of the disordered carboxylic acids in the two structures track well with their dimer O···O separations. This is longer by 0.023 Å in the structure of the title compound than in that of benzoic acid. A database search was conducted and used for comparison of the title compound to other high-quality structures of bicyclo[1.1.1]pentane-containing species.