Infrared matrix isolation and theoretical studies on glutarimide

Infrared spectra of glutarimide isolated in low-temperature Ar and Nz matrixes are reported. The molecular structure, vibrational frequencies, and infrared intensities of glutarimide are calculated with ab initio Hartree-Fock and second-order Moller-Plesset perturbation (MP2) methods as well as with density functional theory (DFT) using the nonlocal gradient corrected functional (BP86). The best overall agreement between the calculated and experimental spectra has been obtained at the MP2/D95V** level. Unequivocal assignment of the experimental infrared bands is performed on the basis of the potential energy distribution (PED). A striking similarity is noted for frequencies of the corresponding CO and NH vibrations in glutarimide and in uracil, thymine, and their methyl derivatives. Furthermore, the significant flattening of the glutarimide ring, predicted by calculations, indicates its structural resemblance to pyrimidine bases. It is suggested that some glutarimide drugs are able to intercalate between nucleic base pairs in the DNA helix or they may act as antagonists of uracil and thymine in biological processes.