Study of p-(3-carboxymethyl-1-adamantyl)calix[4]arene and tetrapropoxy-p-(3-carboxymethyl-1-adamantyl)calix[4]arene by vibrational spectroscopy and DFT

The IR and Raman spectra of p-(3-carboxymethyl-1-adamantyl)calix[4]arene (1) and tetrapropoxy-p-(3-carboxymethyl-1-adamantyl)calix[4]arene (2) were studied. In the IR spectra of crystals and solutions of calixarenes, there is no band of stretching vibrations of free OH groups. In the IR spectrum of compound 1 in the crystalline state, an intense wide band is observed at 3187 cm−1. In the IR spectrum of a dilute solution in CCl4, this band shifts to 3118 cm−1. The carboxyl groups form cyclic dimer or tetramer complexes.The formation of dimers of carboxyl groups is more favorable than for cyclic tetramers. The energy difference is 33.8 and 53.0 kJ/mol in compounds 1 and 2, respectively. The calculation showed that molecules 1 and 2 of dimeric and tetrameric complexes assume the cone conformation. The molecules of compound 2 are in the cone conformation even in the absence of hydrogen bonds along the lower rim.