STRUCTURAL STUDIES OF STRAINED CYCLIC ESTERS . CATECHOL SULFATE

The crystal and molecular structure of catechol cyclic sulfate, C6H4SO4, has been determined by a single-crystal three-dimensional X-ray diffraction study. This material crystallizes in space group Aba2 with lattice parameters a = 15.217 ± 0.010, b = 16.167 ± 0.010, and c = 5.562 ± 0.003 Å, giving a calculated density ρ = 1.671 g cm−3 for Z = 8. The intensities of 687 unique reflections were measured using the θ-2θ scan mode of a Picker automatic diffractometer (Cu Kα radiation). The structure was solved from the Patterson function and refined by full-matrix least squares to a final discrepancy index R1 = 0.090 for 635 reflections above background. The S, O, and C atoms were assigned anisotropic thermal parameters, and the hydrogen atoms were refined isotropically. Angles in the five-membered ring show the effects of strain: the O-S-O bond angle of 97.1° is substantially below the tetrahedral angle of 109.5°, the O-C-C angles of 110.7 and 112.5° are well below the 120° angle preferred by sp2 carbon, and the S-O-C bond angles are 108.6 and 108.7°. The exocyclic S-O bond distances are 1.380 and 1.392 Å, the S-0 bonds in the ring are 1.585 and 1.601 Å, and the C-O distances are 1.398 and 1.409 Å. The most unexpected feature of the structure is the distortion of the five-membered ring to a nonplanar envelope structure where the sulfur atom lies 0.249 Å above a plane through the six carbon atoms and the two ring oxygen atoms. This result suggests that lone-pair repulsions may play a role in the extraordinarily high rates of alkaline hydrolysis exhibited by five-membered cyclic esters of sulfur and phosphorus as compared to their six-membered or acyclic analogs. © 1969, American Chemical Society. All rights reserved.