Solids Modelled by Crystal Field Ab Initio Methods. IX. Stereoselective Order-Disorder in Tri-ortho-thymotide-3-Buten-2-ol (2/1) Clathrate

摘要

Geometries of 3-buten-2-ol (CH3-CHOH- CH=CH2) were optimized using standard ab initio SCF-LCAO-MO methods, as well as the electrostatic crystal field (ECF-MO) approach. Comparisons are made between isolated butenol molecules and molecules packed in a tri-ortfio-thymotide (TOT) clathrate, 1,7,13-trimethyl-4,10,16-tris(1 -methylethyl)-6tf, 12H, 18//-tri-bsnzo[b,f, jM ,5,9]trioxacyclododecin-6,12,18-trione. Excellent agreement is obtained with available microwave and diffraction data. Despite the neglect of orbital overlap between neighbouring molecules, all the significant geometric differences between the gas phase and the solid state are well reproduced. Specifically we note the differences in C=C-C-O torsion angles. The presence of both R and S configurations in the TOT-clathrate with a low degree of chiral discrimination has been experimentally verified. From the difference in calculated molecular energy between the two butenol enantiomers that were optimized within the TOT-clathrate, the observed enantiomeric excess of 4-6% in favour of (R)-butenol is reproduced.