meso-Tetrahydropyranylperoxides: molecular structures in solution, in the crystal, and by DFT calculations and their isomerization to the racemate.
The crystalline peroxide 3a is the main product (out of 10 theoretically possible) from the aerial peroxidation of all-cis-2,4,6-trimethyltetrahydropyran (2a). It has a similar structure both in solution and in the crystal as shown by nuclear Overhauser effects and X-ray analysis, respectively. Theoretical calculations at a density functional theory level (B3LYP/6-31G) provide insight into the stabilities of the different stereoisomers of this peroxide, accounting for the facile, acid-catalyzed isomerization from the meso form to the racemate. Peroxide 3b, which is the 2-tert-butyl analogue of 3a, out of 22 theoretically possible isomers, crystallizes in a similar meso form. As a result of crystal packing effects and the intrinsically (axial) chiral peroxy "chromophore" that deviates slightly from the antiperiplanar conformation, both enantiomorphic forms of 3b are encountered in the lattice.
Balaban
Teodor Silviu
TS
Forschungszentrum Karlsruhe, Institute for Nanotechnology, Postfach 3640, D-76201 Karlsruhe, Germany. silviu.balaban@int.fzk.de
Eichhöfer
Andreas
A
Ghiviriga
Ion
I
Hugo
Holger
H
Wenzel
Wolfgang
W