Which of the following statements about the conformational flexibility of calixarenes is true?
1
Calixarenes adopt only a single, rigid conformation due to the rigid phenolic rings.
2
Calixarenes exhibit flexibility due to the free rotation of sigma bonds at the methylene bridges.
3
Calixarenes have no conformational flexibility and are always in a boat-like form.
4
Calixarenes are unable to interact with guests due to their rigid structure.