Lessons from the mistaken origin of the rotational barrier in ethane


Peter R. Schreiner, prs@org.chemie.uni-giessen.de, Institute of Organic Chemistry, Justus-Liebig University, Heinrich-Buff-Ring 58, Giessen, 35392, Germany
The origins of the rotational barrier of ethane is an old, yet much debated subject that is essential to just about any form of structural organic chemistry, from the conformational analysis of simple alkanes to protein folding. Recent papers re-ignited the debate about the relative importance of hyperconjugative interactions vs. more commonly invoked steric repulsion. It should also be noted that the finding of a rotational barrier in ethane does not originate from the important work of Pitzer and Kemp (1936) but goes back to Ebert (1929) and Wagner (1931); Wilson (1933) was the first to estimate the rotational barrier to be about 3 kcal/mol. The present talk will present an outline of the increasingly detailed understanding of the barrier to rotation in ethane, and serves as an introduction of the two speakers immediately thereafter. New experimental data on related systems will also be discussed.