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

Abstract

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.

Keywords

• racemization
• high barrier
• ring inversion
• hindered rotation
• chiral chromatography
• eight membered rings