Determination of the Very High Barriers to Conformational Processes by the Neat Racemization Technique. Part 1: Barriers to Ring Inversion in Dibenzo [a,c] Dinaphtho [2,3-e; 2,3-g] Cyclooctatetraene and Hindered Rotation in 2,2'-Dimethyl Binaphthyl
1Department of Chemistry, Faculty of Science, Tehran University, P.O. Box 14328-12345, Tehran, I.R. IRAN
2Organic Chemistry 1, Chemical Center, Box 124, S-221 00 Lund, SWEDEN
3Department of Chemistry, Tulane University, New Orleans, LA 70118, USA
4Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, HONG KONG
A method is described by which it is possible to determine the high barrier to ring inversion and hindered rotation by neat racemization of optically active compounds when the racemization is caused by ring inversion or hindered rotation. The method is based preparation of sufficiently pure enantiomers, mainly by chromatography on swollen microcrystalline triacetylcellulose (TAC). By this technique the barrier to ring inversion in dibenzo [a,c] dinaphtho [2,3-e; 2,3-g] cyclooctatetraene, a tetrabenzocyclooctatetraene analogue, was determined to be 67.2±0.8 kcl/mol, a record as the highest conformational barrier ever reported. The barrier to hindered rotation in 2,2'-dimethyl binaphthyl was determined by this method to be 49.5±0.5 kcl/mol.