Dynamic stereochemistry of 2,3,12,13-tetrathia- and -tetraselena[4,4]metacyclophanes

2,3,12,13-Tetrathia- and -tetraselena[4,4]metacyclophanes exhibit temperature dependent 1 H nmr spectra in which the methylene resonances change from AB spectra in the low temperature limit to singlets at higher temperatures. Coalescence temperatures are 256 and 208 K, respectively, and a complete line-shape analysis yields and . The spectra and thermodynamic data are interpreted in terms of a mechanism involving interconversion of syn conformers with little or no involvement of the anti conformers previously assumed to dominate in this type of molecule.