X-ray crystal structure determination and NMR solution studies of 3′,3″5′,5″-tetrabromophenolphthalein ethyl ester

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Abstract

The crystal structure of 3′,3″,5′,5″-tetrabromophenolphthalein ethyl ester (TBPE) has been determined by X-ray diffraction at room temperature. This compound crystallizes in space group [Formula: see text], with a = 12.361(4), b = 12.533(4), c = 9.986(2) Å, α = 99.57(3), β = 112.76(2), γ = 100.73(3) °, and Z = 2. The structure was solved by direct methods and refined by full-matrix least-squares calculations to a residual of 0.034 for 1862 observed reflections. TBPE is propeller shaped about the central carbon and crstallizes with one molecule of benzene solvent per asymmetric unit. In 1:1 CD 2 Cl 2 :CDCl 3 solution complete 1 H and 13 C NMR signal assignments have been made via 1 H 1 H COSY and 1 H 13 C HETCOR experiments. The quinoidal and phenolic integrities are retained on the NMR timescale. By contrast for an acetone-d 6 solution only 14 13 C resonances are found and the colour of the solution changed from green to dark blue. These changes in acetone solution are attributed to the presence of a trace of base which induces the loss of the phenolic proton of TBPE and the existence of resonance forms which render the phenolic and quinoidal rings equivalent. Key words: crystal structure, NMR, 3′3″5′5″-tetrabromophenolphthalein ethyl ester.

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