Phenolphthalein and 3',3''-Dinitrophenolphthalein

Phenolphthalein, C₂₀H₁₄O₄, crystallized in the non-centrosymmetric space group Pna2₁ with two crystallographically inequivalent molecules. Each of these is linked to four others of its own type by four hydrogen bonds having O_donor...O_acceptor distances ranging from 2.631 (4) to 2.787 (4) Å. While chains of hydrogen bonds propagate in a number of directions in this structure, cyclic hydrogen bonding is not observed. 3′,3′′-Dinitrophenolphthalein, C₂₀H₁₂N₂O₈, crystallized in the centrosymmetric space group Pbcn with a single molecule in the asymmetric unit. Each molecule is linked to three others by four hydrogen bonds having O_donor...O_acceptor distances ranging from 2.572 (4) to 3.274 (3) Å. Although chains of hydrogen bonds are prominent in this structure, cyclic hydrogen bonding also occurs and forms dimers. As expected on the basis of the excess of potential acceptor O atoms over donors in both structures, significant C—H...O interactions are also abundant.

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