Letter | Published:

Infra-Red Spectrum of CnD2n + 2 and the 'Long-Chain Frequency' in Paraffins

Nature volume 159, pages 739740 (31 May 1947) | Download Citation



THE most characteristic feature in the infra-red spectrum of any long-chain paraffin (CnH2n + 2) is a strong band near 14µ (725 cm.-1). It was first noted by Coblentz1, but Lecomte2 and many other workers have directed attention to it, while an extensive investigation of hydrocarbons at Oxford and Cambridge3 during the War showed that any molecule containing the group —(CH2)n.CH3, in which n is equal to or greater than 3, possesses this band. So far as we are aware, no satisfactory interpretation of this 'long-chain frequency' has yet been given4, although it has been frequently assumed that it arises from a 'skeletal' vibration of the carbon atoms in the chain. The difficulty about this assignment is that the magnitude of the frequency is rather low for it to belong to a stretching mode of the carbon chain, and distinctly too high for it to be a deformation vibration. Recently, it has been suggested5 that it is due to the overtone of a deformation vibration.

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  1. 1.

    , Astrophys. J., 20, 207 (1903); Phys. Rev., 16, 385 (1903).

  2. 2.

    , "Le Spectre Infrarouge" (Paris, 1928), also Lambert.

  3. 3.

    , and , to be published shortly.

  4. 4.

    For example, , , and , J. Chem. Phys., 8, 143 (1940).

  5. 5.

    , J. Chem. Phys., 14, 614 (1946).

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  1. Laboratory of Colloid Science, Cambridge. March 29.

    •  & G. B. B. M. SUTHERLAND


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