Letter | Published:

Evidence for Intramolecular Attraction between Hydroxyl and Carbonyl Oxygen Atoms

Naturevolume 169pages11051106 (1952) | Download Citation



THE accurate crystal structure analyses of α-oxalic acid1 and oxalic acid dihydrate2 show that the length of the central C—C bond is indistinguishable from the single bond-length of 1.5445 A. in diamond within a probable limit of ± 0.025 A. It is inferred that there is no appreciable degree of π-conjugation across the central bond, presumably because of polarization of the carbon 2p electrons by the oxygen atoms; some other explanation must therefore be sought for the fact that the oxalic acid molecule is perfectly flat in both α and β anhydrous forms and in the dihydrate. It seems unlikely that in all three crystal structures the intermolecular hydrogen-bonding system should be specifically that of lowest energy only when the molecules are planar. In both the α anhydrous form and the dihydrate, the C—O bonds are distinguishable in length, one tending towards a double bond, the other towards a single bond. The centre of symmetry of the molecule requires a trans relationship between the bonds as in (I).

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  1. 1

    Cox, E. G., Dougill, Marion and Jeffrey, G. A. (unpublished work).

  2. 2

    Ahmed, F., and Cruickshank, D. W. J. (unpublished work).

  3. 3

    Stern, F., and Beevers, C. A., Acta Cryst., 3, 341 (1950).

  4. 4

    Parry, G. S., Acta Cryst., 4, 131 (1951).

  5. 5

    Beevers, C. A., and Hughes, W., Proc. Roy. Soc., A, 177, 251 (1941).

  6. 6

    Cochran, W., Acta Cryst., 4, 376 (1951).

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  1. Department of Inorganic and Physical Chemistry, University of Leeds

    • G. A. JEFFREY
    •  & G. S. PARRY


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