Role of Ring Ortho Substituents on the Configuration of Carotenoid Polyene Chains

The 9-( Z )-configuration was exclusively obtained in the carotenoid polyene chain irrespective of olefination and disconnection methods for terminal ortho -unsubstituted benzene rings. The 2,6-dimethyl substituents in the terminal rings secure an all-( E )-polyene structure. The single molecular conductance of the pure 9-( Z )-carotene was measured for the first time to be 1.53 × 10 –4 ± 6.37 × 10 –5 G 0, whose value was 47% that of the all-( E )-carotene ((3.23 × 10 –4 ) ± (1.23 × 10 –4 ) G 0 ).