Absolute Conformations of the (−)-[9](2,5)Pyridinophane Molecule

✍ Scribed by Maxim Fedorovsky; Hans Gerlach; Werner Hug

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: German
• Weight: 627 KB
• Volume: 92
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200900023

✦ Synopsis

Abstract

9Pyridinophane was first synthesized, and its enantiomers were separated, more than 40 years ago, but the molecule's absolute conformations could not be determined up to now. We show here, by the comparison of measured and computed vibrational optical activity (VOA), that the CIP descriptor (P) applies to the (−)‐enantiomer. This assignment is based on the VOA of bands from vibrations localized on the pyridine ring bent by the tense (CH~2~)~9~ chain extending from position 2 to 5. The VOA of vibrations localized on the chain is in agreement with this assignment. Its behavior differs from the VOA of the bent pyridine ring, and conclusions drawn from the chain's VOA alone would not be sufficient, because the close‐to‐enantiomorphic geometries of the chain present in some of the 14 conformers of (−)‐9pyridinophane lead to VOA with an opposite sign. Understanding of how VOA is generated is crucial for the unambiguous assignment of the molecule's absolute conformations.