A 13C nuclear magnetic resonance study of [n]paracyclophanols: chemical shifts and spin–lattice relaxation

Abstract

¹³ C Chemical shifts and ¹³C spin–lattice relaxation times (T₁) of symmetric [9]–[15]paracyclophanols are observed in CDCl₃. Assignment of the aliphatic bridge carbons is performed by the use of Eu(fod)₃ and by assuming additivity of the usual substituent parameters. The aliphatic and aromatic carbon shifts are not sensitive to differences in the geometry of the carbon skeleton. The aromatic tertiary carbons are non-equivalent when internal rotation of the benzene ring is slow or inhibited. The T₁ data are explained in terms of conformational flexibility, intermolecular association, and internal rotation.