Prelog strain

Cyclodecane in its lowest energy conformation. The red triangle indicates three hydrogens responsible for transannular strain. There is an identical interaction on the back of the molecule, as well.

In organic chemistry, transannular strain (also called Prelog strain after chemist Vladimir Prelog) is the unfavorable interactions of ring substituents on non-adjacent carbons. These interactions, called transannular interactions, arise from a lack of space in the interior of the ring, which forces substituents into conflict with one another. In medium-sized cycloalkanes, which have between 8 and 11 carbons constituting the ring, transannular strain can be a major source of the overall strain, especially in some conformations, to which there is also contribution from large-angle strain and Pitzer strain.[1][2] In larger rings, transannular strain drops off until the ring is sufficiently large that it can adopt conformations devoid of any negative interactions.[1][3]

Transannular strain can also be demonstrated in other cyclo-organic molecules, such as lactones, lactams, ethers, cycloalkenes, and cycloalkynes. These compounds are not without significance, since they are particularly useful in the study of transannular strain. Furthermore, transannular interactions are not relegated to only conflicts between hydrogen atoms, but can also arise from larger, more complicated substituents interacting across a ring.

  1. ^ a b Smith and March, March's Advanced Organic Chemistry, John Wiley & Sons Inc., 2007, ISBN 978-0-471-72091-1
  2. ^ Raphael, R.A. (1962). "Proceedings of the Chemical Society. March 1962". Proceedings of the Chemical Society: 97. doi:10.1039/PS9620000097.
  3. ^ Anslyn and Dougherty, Modern Physical Organic Chemistry, University Science Books, 2006, ISBN 978-1-891389-31-3