MOLECULAR RODS - SYNTHESIS AND PROPERTIES

Our earlier synthetic methodology affording bicyclo[2.2.2]octyl [1]-rod and [2]-rod systems proved inadequate for [41-rods. New synthetic approaches were developed, and [3]- and [41-rod molecules were obtained. Sodium-potassium coupling was employed to afford the longer rod units. A radical anion approach gave lower yields. Hybrid rods with aromatic rings interposed were also synthesized. Rods of 9.2-, 9.7-, 13.4-, 13.9-, and 18.2-angstrom length were included in this study. Consideration of rod chirality suggests each bicyclooctane rod unit to be stereogenic, either P (clockwise) or M (anticlockwise). Thus, in a [1]-rod there are enantiomers and in a [2]-rod there are diastereomers. Molecular mechanics treatment of rod stereoisomerization was carried out. Interconversion of enantiomers of the [l]-rod and diastereomers of the [n]-rods should be very rapid at room temperature. X-ray analysis of the 4,4'-dimethoxy-[2]-rod reveals an achiral conformation. AMI quantum mechanics computations were carried out on [n]-rod radical cations and bridgehead cations.