Henry Rzepa's Blog

By about C₁₇H₃₆, the geometry of “cold-isolated” unbranched saturated alkenes is supposed not to contain any fully anti-periplanar conformations. [1] Indeed, a (co-crystal) of C₁₆H₃₄ shows it to have two-gauche bends.[2]. Surprisingly, the longest linear alkane I was able to find a crystal structure for, C₂₈H₅₈ appears to be fully extended[3],[4] (an early report of a low quality structure for C₃₆H₇₄[5] also appears to show it as linear).^‡ Here I explore how standard DFT theories cope with these structures.

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References

1. N.O.B. Lüttschwager, T.N. Wassermann, R.A. Mata, and M.A. Suhm, "The Last Globally Stable Extended Alkane", Angewandte Chemie International Edition, vol. 52, pp. 463-466, 2012. https://doi.org/10.1002/anie.201202894
2. N. Cocherel, C. Poriel, J. Rault‐Berthelot, F. Barrière, N. Audebrand, A. Slawin, and L. Vignau, "New 3π‐2Spiro Ladder‐Type Phenylene Materials: Synthesis, Physicochemical Properties and Applications in OLEDs", Chemistry – A European Journal, vol. 14, pp. 11328-11342, 2008. https://doi.org/10.1002/chem.200801428
3. S.C. Nyburg, and A.R. Gerson, "Crystallography of the even <i>n</i>-alkanes: structure of C₂₀H₄₂", Acta Crystallographica Section B Structural Science, vol. 48, pp. 103-106, 1992. https://doi.org/10.1107/s0108768191011059
4. R. Boistelle, B. Simon, and G. Pèpe, "Polytypic structures of n-C28H58 (octacosane) and n-C36H74 (hexatriacontane)", Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, vol. 32, pp. 1240-1243, 1976. https://doi.org/10.1107/s0567740876005025
5. H.M.M. Shearer, and V. Vand, "The crystal structure of the monoclinic form of n-hexatriacontant", Acta Crystallographica, vol. 9, pp. 379-384, 1956. https://doi.org/10.1107/s0365110x5600111x