The Crystal Structure of Cyclooctatetraenecarboxylic Acid‘ David P. Shoemaker, Hubert Kindler,* William G . Sly, and Ramesh C. Srivast ava Contribution f r o m the Department of Chemistrjj, Massachusetts Institute of Technology, Cambridge, Massachusetts. Received October 19, 1964 The crystal structure of 1,3,5,7-cyclooctatetraenecarboxylic acid has been determined by X-ray diffraction analysis. The crystals are monoclinic, space group C2h5-PZ1/c (with a. = 6.76, bo = 14.64, and cg = 8.37 A.; p = 110” 9.5‘) and the unit cell contains four molecules. The cyclooctatetraene ring is tub form, conforming closely to the DBd symmetry found by gas phase electron diffraction work. The mean double-bond and single-bond distances in the ring are 1.322 and 1.470 A., respectively, with estimated standard deivations of 0.005 A., and the mean interbond angle in the ring is 126.4”, with an e.s.d. of 0.4”. The molecules are present as hydrogen-bonded dimers, with an 0 - H . . . O distance of 2.604 A.
as could reasonably be desired and the results are reported here. Experimental
A sample of COT acid was kindly provided by Professor A. C. Cope. Crystals, grown by sublimation onto the walls of a test tube, were in the form of monoclinic plates or laths perpendicular to the b axis and Table I. Atomic Positional Coordinates --Atom-No.
X Y Kind
1
Introduction This study of the crystal structure of 1,3,5,7-cyclooctatetraenecarboxylic acid3 (hereinafter referred to as
2 3
,c=c\
f F ,C-C-OH i
C,
C=C
4
II 0
5
COT acid) was undertaken in 1952 in view of the then current interest and controversy concerning the shape of the cyclooctatetraene (COT) ring in the hydrocarbon itself. That controversy is now history; notwithstanding infrared and Raman spectroscopic evidence adduced for a crown configuration of D4 symmetry in the vapor state,4 there now seems to be little doubt that a “tub” configuration of DZdsymmetry with alternating single and double bonds is the correct one. This has been shown by electron diffraction studies in the vapor state5-’ and by X-ray diffraction studies in the solid state.* Our early results for COT acidg showed indeed that the COT ring in this compound has the “tub” configuration. Refinement of this structure took place sporadically over an unusually long period. It is now as complete ( I ) This work was done in part under a Grant-in-Aid from E. I. d u Pont de Nemours Co., and in part under Grant A2400 (GM-10850) from the National Institutes of Health. Computations welledone in part o n XRAC at Pennsylvania State University and in part at the M.I.T. Computation Center. (2) Participation in this work was sponsored by the Foreign Student Summer Project, Massachusetts Institute of Technology. (3) A. C. Cope, M . Burg, and S. W. Fenton, J. Am. Chem. Soc., 74, 173 (1952). (4) E. R . Lippincott, R. C. Lord, and R. S. MacDonald, ibid., 73, 3370 (1951). (5) K. Hedberg and V . Schomaker, Abstracts, American Chemical Society Meeting, San Francisco, Calif., March 1949. , 65 (1952). (6) 1. L. I
