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Hyperconjugation not steric repulsion leads to the staggered structure of ethane


Many molecules can rotate internally around one or more of their bonds so that during a full 360° rotation, they will change between unstable and relatively stable conformations. Ethane is the textbook example of a molecule exhibiting such behaviour: as one of its two methyl (CH3) groups rotates once around the central carbon–carbon bond, the molecule will alternate three times between an unstable eclipsed conformation and the preferred staggered conformation. This structural preference is usually attributed to steric effects1,2,3,4,5,6,7; that is, while ethane rotates towards an eclipsed structure, the electrons in C–H bonds on the different C atoms are drawing closer to each other and therefore experience increased repulsion, introducing a rotation barrier that destabilizes the eclipsed structure8,9. Stabilization of the staggered structure through rotation-induced weakening of the central C–C bond10 and hyperconjugation11,12 has been considered to be involved, but evaluation of the contributions of these effects to ethane's internal rotation barrier and conformational preference remains difficult13,14. Here we report a series of ethane structure optimizations, where successive removal of different interactions indicates that ethane's staggered conformation is the result of preferential stabilization through hyperconjugation. Removal of hyperconjugation interactions yields the eclipsed structure as the preferred conformation, whereas repulsive forces, either present or absent, have no influence on the preference for a staggered conformation.

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Figure 1: Ethane energetics.
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  1. Jones, M. Jr Organic Chemistry (W. W. Norton & Company, New York, 2000).

    Google Scholar 

  2. Carey, F. A. Organic Chemistry (McGraw Hill, New York, 2000).

    Google Scholar 

  3. McMurry, J. Organic Chemistry (Brooks/Cole, Thomson Learning, New York, 1999).

    Google Scholar 

  4. Vollhardt, K. P. C. & Schore, N. E. Organic Chemistry: Structure and Function (W. H. Freeman and Company, New York, 1998).

    Google Scholar 

  5. March, J. Advanced Organic Chemistry (John Wiley & Sons, New York, 1992).

    Google Scholar 

  6. Loudon, G. M. Organic Chemistry (Benjamin/Cummings, Menlo Park, California, 1988).

    Google Scholar 

  7. Carey, F. A. & Sundberg, R. J. Advanced Organic Chemistry (Kluwer Academic/Plenum, New York, 2000).

    Google Scholar 

  8. Sovers, O. J., Kern, C. W., Pitzer, R. M. & Karplus, M. Bond-function analysis of rotational barriers: ethane. J. Chem. Phys. 49, 2592–2599 (1968).

    Article  ADS  CAS  Google Scholar 

  9. Christiansen, P. A. & Palke, W. E. A study of the ethane internal rotation barrier. Chem. Phys. Lett. 31, 462–466 (1975).

    Article  ADS  CAS  Google Scholar 

  10. Bader, R. F. W., Cheeseman, J. R., Laidig, K. E., Wiberg, K. B. & Breneman, C. Origin of rotation and inversion barriers. J. Am. Chem. Soc. 112, 6530–6536 (1990).

    Article  CAS  Google Scholar 

  11. Brunck, T. K. & Weinhold, F. Quantum mechanical studies on the origin of barriers to internal rotation about single bonds. J. Am. Chem. Soc. 101, 1700–1709 (1979).

    Article  CAS  Google Scholar 

  12. Reed, A. E. & Weinhold, F. Natural bond orbital analysis of internal rotation barriers and related phenomena. Isr. J. Chem. 31, 277–285 (1991).

    Article  CAS  Google Scholar 

  13. Wiberg, K. B. & Rablen, P. R. Comparison of atomic charges derived via different procedures. J. Comp. Chem. 14, 1504–1518 (1993).

    Article  CAS  Google Scholar 

  14. Reed, A. E. & Weinhold, F. Some remarks on the C-H bond dipole moment. J. Chem. Phys. 84, 2428–2430 (1986).

    Article  ADS  CAS  Google Scholar 

  15. Badenhoop, J. K. & Weinhold, F. Natural steric analysis of internal rotation barriers. Int. J. Quant. Chem. 72, 269–280 (1999).

    Article  CAS  Google Scholar 

  16. Goodman, L., Gu, H. & Pophristic, V. Flexing analysis of ethane internal rotation energetics. J. Chem. Phys. 110, 4268–4275 (1999).

    Article  ADS  CAS  Google Scholar 

  17. Weinhold, F. in The Encyclopedia of Computational Chemistry (ed. Schleyer, P. v. R.) 1792–1811 (John Wiley & Sons, Chichester, 1998).

    Google Scholar 

  18. Weisskopf, V. F. Of atoms, mountains, and stars: a study in qualitative physics. Science 187, 605–612 (1975).

    Article  ADS  CAS  Google Scholar 

  19. Badenhoop, J. K. & Weinhold, F. Natural bond orbital analysis of steric interactions. J. Chem. Phys. 107, 5406–5421 (1997).

    Article  ADS  CAS  Google Scholar 

  20. Glendening, E. D., Badenhoop, J. K., Reed, A. E., Carpenter, J. E. & Weinhold, F. NBO 4.0 (Theoretical Chemistry Institute, University of Wisconsin, Madison, 1996).

  21. Frisch, M. J. et al. Gaussian 98 (Gaussian, Pittsburgh, Pennsylvania, 1998).

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We thank R. Sauers for comments. Support by the National Science Foundation is acknowledged.

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Correspondence to Lionel Goodman.

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Pophristic, V., Goodman, L. Hyperconjugation not steric repulsion leads to the staggered structure of ethane. Nature 411, 565–568 (2001).

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