The Molecular and Crystal Structure of the Cyclic Pentamer of Formaldehyde, 1,3,5,7,9-Pentoxecane

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Abstract
The crystal structure of the cyclic pentamer of formaldehyde, 1,3,5,7,9-pentoxecane, has been determined by the X-ray diffraction method. The unit cell is orthorhombic, with a=8.154 Å, b=10.673 Å, c=7.666 Å. The space group is Pbcn, and there are four molecules per unit cell. The structure was refined by the blockdiagonal least-squares method to a final discrepancy factor, R, of 0.049, using 712 reflections observed with an automatic four-circle single-crystal diffractometer. The molecules in the crystals are ten-membered rings with an exact C2–2 symmetry; the torsion angles of the five independent C–O bonds are 72.9°, −118.7°, 84.2°, −123.4°, and 69.8°, and the two halves of the molecule are related by a twofold rotation axis. The averaged C–O bond length is 1.410 Å, and the averaged C–O–C and O–C–O bond angles are 115.6° and 111.8° respectively. The close intramolecular H···H distances are 2.17 Å and 2.20 Å.

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