Binding of nitrophenol isomers to calix[n]arene (n = 4, 6) hosts

Electronic structure, 1H NMR and vibrational spectra of complexes between nitrophenol isomer and calix[n]arene (n = 4 or 6) are obtained from density functional theory. Nitrophenol interacts laterally with calix[4]arene portals and reveals shielding of all aromatic guest protons in the calculated 1H NMR spectra. The intense OH stretching vibration at the 3287 cm−1 of calix[4]arene on complexation splits into two bands separated by ∼30 cm−1. On the other hand, CX[6] host favors encapsulation of nitrophenol isomer via hydrogen bonded interactions. Complexation of p-nitrophenol with CX[6] engenders up-field signals for aromatic protons on confining within the host cavity while those of o- or m-nitrophenol isomers exhibit both shielding as well as deshielding thereby leading to distinct 1H NMR signals. Interaction energy of nitrophenol toward CX[6] host follows the order: p-nitrophenol > m-nitrophenol > o-nitrophenol, which is reflected in the frequency downshift of OH stretching (host) from OH···O interactions.