5-Formyl-13-methyl- and 5,13-diformyl-syn[2.2]metacyclophanes were syn
thesized. Their electronic spectra, DELTAH(not-equal) for their benzen
e ring flipping, and the result of molecular orbital calculations were
compared with those of the 5,13-dimethyl derivative, with the conclus
ion that Coulombic repulsion between two benzene rings is the major fa
ctor controlling the stability of syn conformers.