Informational rigidity in mesitylene-based calixarenes adopting a 1,3-alternate conformation
Paweł Parzuchowski , Volker Böhmer , Silvio E Biali , Iris Thondorf
AbstractTwo chiral derivatives of a mesitylene-based calixarene known to exist in the 1,3-alternate conformation were prepared by the attachment of homochiral residues to the four exo-hydroxy groups. Thus, the enantiotopic protons of the central scaffold became diastereotopic, leading to a doubling of their 1H NMR signals in one example. From the temperature independence of the NMR spectrum, a lower limit of 24.2 kcal/mol could be estimated for the barrier of ring inversion. MM3 calculations confirm the 1,3-alternate conformation as the energy minimum, and estimate a barrier of 25.7 kcal/mol for the 1,3-alternate-to-1,3-alternate* interconversion process. This high barrier is due to the repulsive steric interactions between exo-methyl groups at vicinal rings when these groups pass each other.
|Journal series||Tetrahedron-Asymmetry, ISSN 0957-4166|
|ASJC Classification||; ; ;|
|Publication indicators||= 14; = 14; : 2000 = 1.048; : 2006 = 2.468 (2) - 2007=2.46 (5)|
|Citation count*||13 (2015-10-25)|
* presented citation count is obtained through Internet information analysis and it is close to the number calculated by the Publish or Perish system.